Not getting a work permit implies not working in Thailand implies no local source income.
LOL
Then, as long as this loophole still applies
This is not a loophole, this implies that you aren't managing and operating your own comapany from Thailand because in that case it's local sourced income so the remitting part doesn't matter.
You can believe that you aren't the agent but if you are the only one managing and operating the company you are responsabile for the sales so you are the agent, like it or not.
How high are the chances of getting caught?
Probably low but you need to be aware that you aren't compliant and accept the risks involved.