Depends upon a couple of factors. If your location is London Zone 1 or 2, my experience is that they never ask for a transportation fee as they normally arrive via tube or Uber. Some will have a driver, which I don't really like because the end time is strictly adhered to. It can also depend upon the end time, because if it is late when public transport is no longer a viable option, they might ask. But most professional WG's won't ask for a fee within Zone 1 or 2.
For outcalls, I tend to book someone that is a known quantity rather than TOFTT. I've generally had really good experiences with them showing up on-time, they resemble their pictures, and provide the services stated on their profile. I tend to avoid the nationalities that often times provide dubious services.