There have been a few reports of issues, but given there are ~ 35 + million visitors, it sounds more like a few who are suspected of potentially working illegally.
https://www.thaivisa.com/forum/topic...refused-entry/
https://www.thaivisa.com/forum/topic...ngkok-airport/
I personally do not carry 20,000 THB in cash when I arrive, but I did bring my Bangkok Bank bank-book with me on my most recent trip, in case I had to prove anything. I'm on a One-Year Extension of Stay based on Retirement, with a Multiple-Entry Re-entry Permit.
Entry is up to the whim of the Immigration Officer, and can be denied for any reason, which does not have to be given.
I'm not sure this is something to be concerned about for most tourists, with a visa, or from a Tourist Visa Exemption country?
I think that, for those who require a Visa on Arrival
http://www.consular.go.th/main/th/cu...itled-for.html
they may be more strict/inquisitive re: funds on hand?