Especially for the ones of you who trade en masse for large number of dolls.
Double-check the trade(s) before accepting because sometimes, your partner can be confused and throw a plushie/beanbag instead of a lifelike doll and you're one-off in what should have been an even trade.
I'd say 99% of the time, it's an honest mistake and communication is key. But, still, always check the trade to make sure it is indeed what you agreed on.
It happened to me a couple times, and I made countless number of trades. :D