If you reset the same trap you just caught the 'possum with, you should be ok. The reason is because that whole little area where he was trapped is saturated with his scent. The only way it wouldn't work out is if the trap had some blood on it. So if you do have a trap you are going to reuse, it helps to give it a dust bath to remove any excess grime, blood and/or scent. By dust bath I mean give it a good scrubbing using the dirt.

Good luck,

iSnipe