Renting sites

Hi.
I am buidling out a few niche sites to be ranked to #1 to rent to businesses. Do you guys know of a place that tracks how much the average lead is worth to a doctor or lawyer? Also are there any "must read" posts on site flipping? Searched a few but didnt see any.

I saw a post sin this section where a member rented his site for monthly payments. Try to search that and you can get an idea.

You can use an online phone services to redirect the calls or the leads to the Biz owner via Twilio or Callfire to track your calls.