Tetrahydrofuran and M.E.K. can smooth PLA. I've used M.E.K. but it tends to take a long time with Inland generic PLA spools (there are different formulations of PLA so be aware that not all PLA is the same). I would strongly urge anyone considering these chemicals to use them near ventilation
I should add - Tetrahydrofuran and M.E.K. make short work of latex gloves. Were suitable gloves when handling.