The other hidden scam in this is that [some/many] these sites will give you X number of free credits when you first sign up. Not only is this to get you hooked

The other hidden scam in this is that [some/many] these sites will give you X number of free credits when you first sign up. Not only is this to get you hooked and using the site but it cheats people who are already hooked and paid for their credits because it allows others to bid and "take away the winning bid(s) of actually paying customers) for free!