I've zero problem selling / replying to messages from Thais. In fact as I type this I remember in 2017 I sold an electric Wok to a Thai guest house owner in Chiang Mai????. He messaged, we arranged to meet and he collected all within about 2 hours.
HOWEVER:- In the past 12 months I've listed 5 items on FB marketplace (in CM and Pattaya). I must have had 30+ messages from Thais, to which I always reply but 95%+ never respond.
Of my 5 listings, 3 have sold, 1 to a girl from UK, 1 to a Korean and 1 to a Russian.