The Polymaker machine is just using IPA, their trick is in the filament, but I don't like being locked in to a brand like that.
As Jim said, there is no easy chemical method, THF is probably the safest but the results will not be as good as that with acetone and ABS. IMO that always looked kind of 'melted' anyway.
With PLA, the general rule of thumb I use is if I am going to sand it, then I am committed. When it comes to PLA, there is no such thing as just 'a little sanding' and calling it good. It's all or nothing, as once the grit hits the plastic, it is going to go chalky on you. It seems tedious, but it really is faster to work up through the grits i.e. 240, 320, 600 as each one will knock off the peaks of previous layer lines. From there, a low-build filler/primer if you are going to paint. Or another 600 -> 1200 wetsanding if you want to leave as is with a clearcoat.
XTC-3D really does work though if you can get it and want to try it. It's crazy expensive to have shipped overseas so we're out of luck over here.
Other options are two-part resin coatings, those work too. It all depends on the piece and what the final use will be.