There is always the possibility for anybody to scam anybody, generally we do not get too many of them these days as it is more profitable to run a shop rather than scam people. Shoptemp is an actively managed directory but equally there are free options for it and any measures the shoptemp curators take is reactionary.
I would like to say that people signing up to shoptemp is a good sign but it is also the case that shoptemp is the only thing like it in the flash cart/modding/console repair world that I know of (what few sites remain and keep updated seem to have sponsors they work hand in hand with, are the fronts for an actual shop or have their own small shops).
If they are a gold account ( http://shoptemp.net/country/All/?sort=account ) then they are setting up a groundwork for their site (traditionally one tells the scammers/unreliable apart from the real thing/reliable by seeing which ones invest in their infrastructure rather than have a slapdash leased infrastructure). However, shoptemp gold membership is more money on top of an already expensive entry into the flash cart world (you have several thousand dollars worth of setup costs if you are going to try buying stock in after all) and is far from mandatory so not all will do it.
Likewise we do have the reviews thing for a reason. For my money it works much the same as the likes of Amazon reviews in that you check the spelling, grammar, wording and such and decide upon which of the review types to follow.
to put it simply, yes they should be safe.
however most of these stores are in China so you never know.
but if they took the time to register on Shoptemp and are willing to pay a small sum to get their products listed on there, it's likely that they aren't complete scammers