I'm not sure what you mean by "resale" but if it relates to consignment items where the store sells them for the owner I only know of a couple in the Flo area. One is for children's clothing and items only and it's in the Paddock Hills Center where the post office is (at least I believe it is still there). The other is in old town Florissant and it's called The Blue Rose, I think. I haven't check either of them out in some time so that info might not be correct. There are probably several others in the near area I don't know about.
If you mean thrift stores that just sell clothes, furniture, etc that is used donations then the Salvation Army store in Paddock Plaza is very nice, clean, air conditioned, lots of different things and very reasonable prices. I go there to buy books because I am an avid reader.
Then there is the Goodwill store which is over on Lindbergh/Washington in that big shopping center which I think is called Flower Meadows or something like that. The DMV is in the same center and several other stores. I don't shop there although I've heard it's a nice place, but I think their prices for books and other items are kinda steep for a thrift store.
Hope that helps, maybe someone else has some better info. For anyone who reads and likes to get books at a bargain price you can't beat the St.Ferdinand Shrine book sale every Sat. 8 am -12:00 in the old school house. Big selection and really cheap, all the money goes for the upkeep of the shrine.