I think what you and the OP posted has anything to do with Apple setting up a "scam". If it's really a scam, there's no chance in hell I would have gotten my $200 back exactly as they quoted me. For the exact same iPhone (which is a 6S) as the OP. The OP's title of this thread alone is a big assumption, the assumption that this was some scam sting operation by Apple. And yet I got my money by following their trade-in program instructions.
Just because you had a positive experience doesn't negate the less-than-positive experiences of others.
There are plenty of Better Business Bureau complaints about people receiving much lower quotes once their devices were received by Phobio.
https://www.bbb.org/us/ga/atlanta/profile/ecommerce/phobio-llc-0443-27756683/complaints
Neither the OP nor bbdenarz stated Apple is running a "scam sting operation." But a third party is involved, and it doesn't sound like Apple is stepping up when the third party (Phobio) is disappointing customers. In the title, the OP stated the promotion is a scam, and it may well be, given the number of users who have complained.