Her exact explanation was, along as you are outside of Thailand more than you are inside over the year and have gaps between your visits then you will be viewed as a tourist
Your agent is talking utter nonsense. I returned yesterday into Suvarnabhumi, 5th Stamp on arrival this year average stay 5 weeks a time and no issue atall. Asked the nice lady on the desk she said its all rubbish. It's border runs they are targeting nothing else.
I've got one, had no issues myself. Always seems to be someone at check in that thinks the rules don't apply to them. Delays everyone else waiting to get through