i used to be a sales manager for a competing brand and we offered the same premise, except it was meant for financially abled customers, it was somewhat of a bad deal to consumers because they were caught off guard to be honest, the credit is how much they can give you upwards to that amount and not $1,000 as a matter of fact, “Qualifiying unlocked Device” has to meet their requirements to be worth some money and that always meant having a near brand new phone, we always told customers to get it repaired through applecare or Asurion to get the most amount of the trade in, even then *credit* check is a hard one to see how many lines you could do and you would need a perfect phone number, but the threshold is always 3 months to get the credits or gift card with any provider to ensure brand loyalty, ATT, Verizon and Tmobile all want your business but they favor phone numbers from other carriers to meet their monthly quotas.
It’s a shady business but makes their world go around, the trade in part always left people owing more money than they actually owed to be honest and let’s just say some customers never owned their iphones with the forever iphone program sprint used to have….
I'm going by what T-Mobile has actually published here, not whatever your previous company may or may not have done. They say they will pay what you OWE (not what the phone is worth) to your current carrier up to $1000. The idea here is you keep your phone but switch to T-Mobile service (thus their wording - "Keep and Switch"). You're not trading your phone in, so the condition of the phone should be irrelevant to T-Mobile.