Finding people who do not mind being sketched is my purpose, these days. For myself, I have noticed people who work in public place are an excellent choice. They are not going to walk away and usually are at ease with people looking at them. If they give you a smile, a thumbs up or show off a bit …it is a good sign. If they are selling food buy something, playing instruments put money in the hat, sometimes an appreciated smile or show your sketch is enough. Then there are times when you pack up very quickly and move on.