No idea, I am not a tourist in Thailand , I am working so personally I can pass any number of times, it all depends on the officers , some let you go back and other may tell you to go to the embassy of the country you are coming
The only reason to use an agent is all documents in hand before passing the border and not waiting an hour plus to get it done at the check point just for few extra Baht
If you get your insurance at the border you will be stock for an hour plus and after you get your insurance you will get the Malay road tax (free) which is another half an hour