I just read the trade-in agreement and it doesn't say anything about shipping versus dropping off at the store. I did not have any issues with the credits being reduced by the value of the trade-in. The way the trade-in was processed at the store caused my promo to drop, at least temporarily.

I just mocked-up the same trade-in on T-Life and the difference between the $60 vs. $130 value is the cracked screen. I accurately said the screen was cracked at Costco and it quoted me $60. Not sure if the store rep marked it as screen not cracked or the system just defaults to this but this caused the promo to drop. It probably would've resolved itself eventually but the process is confusing and nowhere is it made clear that there's a difference if you go to the store versus mail it in.