I'm am looking to sell completed models but do not want to disassemble them. Can someone point me in right direction?
Welcome. You can sell these easily on EBay, just mention in the description that the sets will be shipped assembled. Two things to keep in mind:
Since most shipping costs are calculated by box dimensions, your shipping costs will likely be higher than when you ship the sets broken down.
Please make sure these sets are NOT glued ... you do not have to mention this in your listing, but absolutely should if they are (even if they are only partially glued).
I have personally bought both assembled used sets as well as disassembled ones, and have no preference. I always disassemble and wash before I reassemble. The only issue I faced was when I bought a set and it turned out to be partially glued, which was not mentioned in the listing. That was an easy SNAD case (Significantly Not As Described) and a full refund from the seller.