Hi,
If you're ever nervous about using a site you're not familiar with, why not look up reviews online? There's plenty of online shopping review sites like Qype etc that allow customers to put on unedited reviews and share their experiences. Of course a lot of bad reviews is usually an indicator that something is amiss.
Additionally, too many good reviews is suspicious. Look at the timing of the reviews, are they too close together? Are the usernames similar? Do they all say pretty much word for word the same thing? These are indicators they've been placed there by the shop themselves.
Other things to watch out for is if they use Secure Online Purchasing symbols, if they have this they'll usually have a crest and certificate they can display on their site.