You're right to be cautious
<< How do we go about checking them out. Some of the offers sound waaaaaaaaaaaaay to good to be true. >>
You have a measure of protection by playing at a casino that uses one of the major, respected software providers, because those providers don't want to be associated with scamsters. For players in the U.S., that mostly means Microgaming, because the other big providers have pulled out of the U.S. market.
But you should be doing additional due diligence. Start with the pages at:
There are lots of cobwebs and dust kittens over there, but these pages are still chock full of essential information. These will give you the basics on how to select a casino, and how to play a bonus profitably. Know that straightforward cashable bonuses are all but obsolete for U.S. players.
Also be sure to see:
Know your edge, and know your bankroll. Have fun!