Can I trust CSTOYS?
 

As the title says, I'm thinking of buying something from their website. Are they legitimate?

I'm assuming you are referring to : http://www.cstoysjapan.com/

If so then yes, they are definitely legit. They even have videos of every package to send showing you whats being packed and how its packed. I haven't ordered from them in a while because there hasn't been anything I've really wanted though so maybe things have changed though I doubt it.

They're legit, but I've had numerous bad experiences with them. Every order, save one, I've placed with them has been screwed up in some way (including the great Lock Seed disaster). Of course, to be fair, there is not one company out there that hasn't had some level of customer dissatisfaction in its history.

I've ordered from them a few times, usually vinyl figures. Even watched the vids of my stuff getting packed up, which is awesome. Their shipping can be a bit pricey though.

Well, given how low their prices are, I would say so. :lolol

Great Lockseed Disaster?

They took a bunch of orders for the Knuckle/Kurokage DX set and required payment in advance. Then they gave Bandai a credit card number for an account with insufficient funds, so their order got cancelled and they were unable to fulfill any of the orders made and already paid for. This also had the effect of denying their customers the Sid Lock Seed, as you had to get the Knuckle/Kurokage set and the previously released Durian/Donguri set from the same place to get Sid's. They apologized, gave out refunds, and a $10 store credit (that I never received) but, in my opinion, it was too little, too late. I think it ended up costing me about $125 more to get the Lock Seeds on the secondary market than it would have if CSToys been on the ball.

I deal with CSToys for several years now and have a very positive opinion of them. Their prices are about equal to what the product really costs, whereas many sellers on Ebay like to bump up their prices, with the reasoning they are selling an "Extremely rare figure, only available in Japan". Shipment is really fast, but, as mentioned on this thread, a bit on the expensive side.
Another thing I really like about this shop is their personal treatment of their customers. Many of my packages came with personal handwritten notes, that included my name, in which the staff thanks me for doing business with them. They also tend to respond to e-mails very quickly.

The downside of CSToys, for me at least, is that it is a very small store. This means popular products can get sold out fairly fast. Especially if they are cheap. A good example for me are the Gaim Arms Change figures. Sometimes they were sold out within five minutes after being placed on the site.