i agree....they do have rules.....as i have experienced myself. I feel if you want to come back n forth...its best to get a proper visa that allows that. A tourist visa wont cut it. You will run out of luck sooner or later!
Often your denied is because you have been into thailand 3 times in 12 months. It says in the rules that can do at least 2 times...however they have turned around a few times and depends who you get on the day. Best thing to do is get a proper visa...