Am I the only one that likes a high class date in a total dump motel?  Brings out the nasty!   
I've  done a bit of light negotiation for multiple hour/multiple girl  services, but isn't really the norm.  I have suggested prices if a  particular rate was not offered up in the ad.  
Double checking  prices, I pretty much always do that with someone new.  And I usually  confirm if I am receiving a grandfather rate.
At the end of the  day, I try not to start the "working relationship" on the foot of trying  to save $50.  That being said, I have been able to afford to be off  Backpage (or Craigslist in its glory days) for a while.  When I was on  there, I was counting my pennies.
As for overcharging?  Well for $750 for 2 hours I would expect gorgeous, flawless body, full PSE up for doing pretty much anything, flawless DD jugs, a fantasy girl persona, and outcall to my house where I can enjoy myself with the pleasures of home.  
...but sometimes you just need to drop the cash to kill the curiosity.