I don't get why anyone would care about seeing what the offer amount is before registering. You enter your email address, password, and say yes or no and you get $10 bucks... it's kind of a no-brainer. What, you're not going to spend 15 seconds registering to get $10 if it is a lowball offer? You tell lowballers to eff off every day via email, why not get paid for them wasting your time?
Like was said earlier, the three guys running this service are beyond reproach. They're not scamming you, phishing for your contact info, or anything nefarious. They're trying to get you paid simply for responding to a purchase inquiry, you should be kissing their feet not throwing a hissy fit. Christ.
Edit: All that said, if you don't know the guys running the service I can see how it would sound too good to be true. But now that you know they are serious players, why not drop it?