As you say, that's about the worst place to be for a border bounce because it's not near any land borders that you can use. Why not just go to Bangkok and take a quick flight out and back in the same day? Generally you will want to aim to go to a country that you have visa exempt entry for and don't have to buy a visa on arrival. It depends on your passport which countries that would be.
Otherwise you're in for a very long day stuffed into a mini-bus van as they drive you to a border, get you stamped out and back in, and then drive you back. That's how land border bounce agencies work.
Is it possible? Yes. Once the visa is issued it doesn't matter where you fly to Thailand from.
But there have been reports of people being asked for follow-up documentation proving they are either in the country or still in the country if the embassy gets any hint that you left. If that happened to you and they found out you left already, they would cancel your application.
so it's definitely a scam. One of the most popular for a long time. After he pays for the medical certificate then there will be another problem that needs 2000 baht. Then after that another problem for 1000. On and on