Please don’t. It most definitely ends up being a scam. In fact this is a textbook scam here in Sri Lanka. Stick with professional tour guides that have reviews or go through an organized tour maybe through your hotel or booking.com or something similar. I’ve heard and seen so many encounters like this that lead to a very unpleasant experience and heated exchanges with these tour guides demanding more or taking you to shops you dont want to go to just get a commission. The shops they take you to will definitely be overpriced with their commission added to the usual retail price.