If you want to learn about spotting scammers, I recommend you take a look at the videos I linked before--Mark Rober's
Glitterbomb, and The Modern Rogue on
Phishing and
419 Scams, as well as their video on
Five Outrageous Con Men. It's not the be-all end-all of research on cons, of course, but they're all very fun to listen to videos that break down how some common scams work, how some very classic scams worked ("I've got a bridge to sell you" was a real thing, but
never that straightforward) and some of the "hallmarks of a con" that can help you spot them when they turn up.
Scams aren't always about getting your money--or they can contain some very roundabout ways of getting your money (watch the Mark Rober video for how the "this is Amazon, your account has been charged $300" scam works, it's fascinating). Or they can be about getting information, classic phishing attacks. Sometimes (often, even) they use tactics of both. Sometimes the goal is to get you to install malware, so your device becomes part of a botnet for sending more malicious emails, or part of a DDoS attack. There are so many reasons people do scummy, scammy things.
In this case, I think Andar probably has the right idea--by getting a game from you, they get something to put their ads in that they didn't have to work on and, if you don't know what to look for in a contract, they'll never have to pay out to you on. Although I think JohnDoeNews has a great point as well--are they packaging spyware into your game? What ads are they going to be showing?
Hmm. It's definitely something to be leery of.
And the QA they mentioned may or may not even exist. As Jack Sparrow said, "you can always trust a dishonest man to be dishonest, honestly." What's one more lie to tell someone they're already lying to? Similarly: it's illegal to wear a bulletproof vest while robbing a bank in New Jersey. That'll solve armed bank robberies in New Jersey! ....
waaaait........
Regardless, once you've been scammed, you'll probably be in for a bunch more attempts. The person that scammed you will sell your email address, phone number--whatever ways they have to contact you, whatever information they have about you--to other scammers, because you're a valid mark.
The short version, unfortunately, is that if it sounds too good to be true, it probably is.