I've sold two iPhones to Gazelle in past years with no issues.
This time, I sent back my iPhone 5 in damn near perfect condition (not a mark on the thing). They just adjusted the offer down by $105 because the screen was cracked. It wasn't cracked when I packed it in THEIR packaging, exactly as THEY instructed me to do. So either their packaging is substandard, or someone on their end cracked my phone, but either way I'm out $105. I'll never use this service again.