The problem could be getting the job done by an agent, say in Pattaya, if you are actually living in a different city, say Chiang Rai. You have a stamp from Pattaya Immigration Office in your passport but you're not living there.
Am I wrong?
How would you deal with it?
Let's say the agent in Pattaya makes your 90 day reports with a fake address, you'd then be a Pattaya resident.
But you're also registered in Chiang Rai, the place you're actually living in.
What if one day you need a residence certificate?
These are the reasons why I'd advise against getting the job done by an agent at an Immigration Office that is not in the city you're living in. Correct me if am wrong.
Cheers