They won't question you until you've done this several times. You never get questioned at immigration when doing a 30 day extension. Just make sure you have a tm30. They'll scam you for 1600 baht if you don't have one. They say it's a landlords responsibility to submit for a tm30 yet they fine us on the spot telling us to be reimbursed by the landlord. A genuine immigration would mail the fine to the landlord. It's a sneaky horrible scam this one but of course easily avoided as long as you make sure it's done. Good luck