Without getting into a long story, lets just say that on a few occasions a few farangs would not take "no" for an answer. Others a "no thanks" does fine and others take a few stabs at it before giving up. I don't think any of these aggressive farangs spoke enough English to get into a protracted conversation over the lack of my interest.
I have never had a problem with a Thai or Asian. One "no" is all it takes. Not that I say that many no's to Thai and Asians.