i changed states recently and had trade in processed at 2 apple stores.I always trade in person at Apple Store, or sell it on Craigslist:FB market place for cash. I personally wouldn’t have sent a phone, which fits the definition of mod. Apple, Verizon, T Mobile and other carriers use third party services.if you have a phone with visible cracks, modded batterg, other issues, trading online is a gamble.
Old state: visual check, pics and that is it.
New state: all above + waiting for apple scan tool to verify all oem battery and screens on the handheld.
To be fair there was 1 year gap between the two, so maybe they did change procedures.
So in this case 3rd party battery wouldn’t fly with in store trade in.