Persistence can't be overdone.
You can't make too many sales calls, you can't become too much of an expert in your product, etc. In the "artful" side of a sales interaction, there is a difference between persistence and being a nuisance - you inherently know the difference. Time and experience will help you differentiate, but the old rule "when it doubt, go for it" applies. Some sales people use not wanting to be a pest as an excuse for their approach avoidance. Persistence obliterates procrastination and demands immediate, direct action. It leverages the "necessity is the mother of invention" power of innovation and imagination. Even if you don't know what to do next, if you persist you will find a way. A way must reveal itself!