It's going to come down to culture, and income differential.
I've found that in countries where bartering is more common, then generally touts are more persistent, as they can keep lowering prices and the like.
However, in other countries where you're the 'money on legs' to the locals, you may find more persistent 'bugging' or chasing down streets, because the payoff for them is huge.
In addition, when tourists are out of their comfort zone, their fears can be used or lack of knowledge taken advantage of, to elicit cash. Overpriced taxi fares, a guide for the 'dangerous streets' and so on.
So in evaluating a country ahead of time, consider if it's generally a poorer country, a very different culture, and considered 'dangerous' by outsiders. As a ROUGH (there are always exceptions and changes!!!) guide, that's an idea.
You can also search the internet for views of touts in the area, but generally more people post bad experiences than good experiences, so take them with a grain of salt.
Disclaimer: Not everyone has the same experience, and reading online will see arguments about how Mexico does or doesn't have bad touts, or how Moroccan ones will chase you down the street - but my description above comes from some experience.