Doctors can actually pay per lead and so can attorneys. However, it is actually "pay per contact" now. This argument has gone on forever, but your not sending them a referral. (which means your compensated if they do biz) You are in fact sending them a contact (paid regardless of they do biz) and you see yourself as a direct extension of Google or a co-marketer of their firm/practice.
One company that is doing this and is in the Inc. 500 is one called Total Attorneys. They sell per contact Bankruptcy leads to attorneys for $50/each.
One of their founders name is Kevin Chern. His company was catching some flack because some attorney filed a class action lawsuit against them saying they were sending attorneys "referrals" however he details how the biz works here. Read the comment section where he defends how his company works. (Look for his name)
Legal Blog Watch
Understanding this will help you bypass all the legal b.s. that has been in marketplace.
As far as getting leads for plastic surgeons, I did this using Facebook. I pretty much copied Shoemoney local affiliate post and it came out good, To test it I offered a "Free Botox" (Shoemoney offered free teeth whitening) and received 9 leads in about 4 days at an avg. cost per lead of like $3
I than approached a docotr and told him what I could do and this is what I found out.
-Dr. could not offer anything for free because of the organization he belonged to didn't allow it. (A way to uphold price/quality in the mkt place)
-Dr. would have to see if clients came back after 6 months (thats how long Botox lasts) So for 6 months he would have to shell out money for my lead price, cost to inject Botox, & his time. Than wait to see his ROI.
-Customer life time value is important but tough to detail considering they have no idea about the avg. cost per lead and customer. PHD but no biz sense.
From my insight. There is just something about offering things for "Free" that brings that certain type of client in the door. The client you don't want.
Fun Fact:
My highest CTR Facebook headline was "New Year, New You."
My highest CTR Facebook picture was a before/after of Botox.
Maybe you may have better luck. Hope you do.
(my bad on the spelling)