1. Get a Paypal Account
The first step you should do for shopping overseas is set up a paypal account; paypal is accepted by most stores in Japan that are willing to ship overseas. I do not fully understand why but many Japan companies prefer not to ship internationally and in those cases another step will be necessary. In either case most Japanese Businesses will prefer to be paid through paypal then with your credit or debit card. To make things simpler you can tie your debit card to your paypal so it can draw money for online purchases directly from your account. Every payment needs to be approve by you, the paypal account holder, so sometimes you will find situations where the seller will ask that you keep an eye out for a bill to be sent to your paypal account sometime after you have sent in an order. Traditionally you need to make this payment before they will place the package in the mail.
Important note about paypal claims; Paypal allows you to file a claim to be refunded (through Paypal; not the seller) if something goes horribly wrong. There is a time-window in which a claim can be filed in order to get a refund so it is important to stay on top of the status of your order. If the problem happens outside of the time window and the seller simply refuses to refund you then there is often no way to get your money back.
2. Save up $20 to $40 USD for Shipping & Handling
Japan, perhaps because it is an island, has very expensive shipping rates and it is often determined by the weight of the package being sent out. Setting aside money separately from what you can spend on the actual items is important to do in advance because sometimes you might want to buy something, might have the money to purchase it, but then you may not have the $20 to ??? dollars to have it actually sent out to you. By saving up a head of time you are giving yourself the freedom to not worry about shipping costs and instead you can then simply focus on the price of items you want to buy.
Important note about the rising cost in imports from Japan; Due to a recent change in Japanese law, consumer tax has risen (as of April 1st 2014) to 8% from 5% which means that Japanese businesses have adjusted their pricing to compensate. On January 1st 2015 the consumer tax will rise again to 10%. This change is going to be reflected in how much products either cost or how much sellers charge for shipping. (It's up to each company how they want to "express" the rise in cost)
3. Know the differences between EMS shipping and Air Mail
It is very important to understand the differences between these two services because while many stores only use one, some businesses may offer you the choice of either of these shipping methods. Two key differences are the price and delivery time.
Air Mail is much cheaper (Bodyline has a flat shipping rate for Air Mail) and EMS can vary based on Weight ($15 to $20 minimum).
In terms of delivery time Air is shipped through a bulk method which means factors not related to when you ordered the item determine when it will ship out. Air Mail can take up to 40 days to arrive due to this so time-sensitive objects are a bad idea for this method. By comparison EMS usually takes under two weeks. My personal advice for this difference is that Air is a good option if you want something eventually but do not need it in the immediate future; while EMS guarantees a smaller time window and allows for easier tracking of the package; in case you need to know exactly when it will be arriving.
The other major difference between EMS and Air Mail is the issue of security; EMS insures the packages and will compensate if the package is lost (it is important to make sure the package is listed at it's correct value in order to do this) while Air Mail guarantees nothing. Depending on what region of the world you live in the issue of making sure you package is insured differs. If you are pretty sure your region is "safe" and has a low theft rate (some countries have low theft rates in their suburban neighborhoods but high theft rates within the postal system) then the likely hood of needing to re-coop from a lost package is low and you might not need to worry about insurance; but if you are in a "high risk" area then insurance might protect you from a long financial recovery.
4. Be aware of Shopping Service Fees
Stores in Japan that refuse to ship internationally can still be accessible through a shopping service or an "ss". A shopping service is an individual or a group of individuals working together who can physically get to the store you want to buy from and purchase the items in person to then ship out to you. There will be a fee and it's usually based on a flat "travel fee"; the cost of transportation (gas for car or bus ticket) and time PLUS a certain % of the total purchase cost (starting at 2% of the total cost). There may or may not also be a fee for the shipping, though how a Shopping Service chooses to list and break-down their fees is unique to each of them.
The three most important things to consider when selecting a Shopping Service is;
A) Feedback from past customers,
B) Communication; their ability converse with you and
C) How their fees compare to other competing Shopping Services
The reason why I listed Feedback before communication or fee rates is that there have been many bogus Shopping Services in the past. Because the person lives far away, often in a different country with different consumer laws, there is a lot of room for them to potentially "take the money and run" (stop replying to messages and just ignore any outreach). It can be very difficult and sometimes impossible to get your money back from a corrupt ss so it is best to read as much feedback as possible before even contacting them. It's even best to go with a more expensive Shopping Service that has good to fantastic feedback then an "okay" one that is sluggish and not as reliable. Reliability is also very important because many store in Japan release things in limited number so it is important for the ss to go to the store and pick up your item before it sells out.
In terms of communication it is very important that a shopping service can understand exactly what item you want, in what size and what color. A good idea is to both send your requests in e-mail form and with pictures attached. Try to get some sort of confirmation that you understand each other before any money has exchanged; sometimes shopping services mean very well but because of the language barrier gigantic mistakes can be made (buys wrong color, wrong size, buys multiples, etc).
Regarding the fees for an ss, as stated above, it's really best to pay more for better service. Don't be swayed by a cheap shopping service; if their prices are too low that is often a bad sign that they may be a scam.
5. Always follow website instructions and take a moment to consider each sentence
Web stores based in Japan either have hired someone to translate their web site or have left browsers like Chrome to automatically do the translation for them. Most of the forums you will see when shopping online will have very blunt and clear statements ("address", "state", "country") but sometimes you will run into a field that requires information that... You just can't make sense of. Before panicking and asking the internet for help; take a moment to try and consider the most literal meaning of the text given to you. If you consider this, but still aren't sure, then it's always okay to take a screen cap (if you can; screen captures are very useful) and go to a place on the internet that can help you.
6. Returns are not very Japanese
Most stores from Japan are reluctant to do refunds for customers. Some stores even refuse to acknowledge when something is defective. So please, please; when ordering overseas do not automatically assume you can return what you receive. It is very important to be sure that what you are ordering is what you truly want and that if it doesn't work out you will not be devastated. Try to mentally come up with a back-up measure if it doesn't work; could you resell it or is their a friend that could fit it better that you could gift it to? Considering these options and having a plan can be really helpful in relieving stress as you wait for your package to arrive.
So those are my six tips for shopping Japanese stores as an international (American) customer. Really the most important thing to take from this list is that importing goods is not an impossibility but it will always be more challenging then shopping within your own country. Please don't feel intimidated to try it out; it's not hard so much as it's just a few more steps.