Usually if they come off as friendly in their profile they'll be cooperative in a trade to! Being detailed in their info under the trade helps to, and I particularly like people who understand when there's a set back and are comfortable telling me when there's one instead of waiting until I ask about it (example your card arrives before mine even though I sent out first and when I ask they say "Oh yeah something came up I sent it out a couple days late") Owning up to mix-up mistakes is good to, it's happened a couple times to me where someone mixes up my card with someone elses. Usually I don't ask for a different card because I wanted THAT card, so making getting it back a top priority and keeping me updated about it also makes me very happy <333
honestly I just try to be very firm about sending video proof. as someone who doesn't have very many proofs, it's weird to be like "show me your proofs!" when I have 3 myself 😭