Huh? You just tell the hotel valet that you want a taxi to whatever location, and that you want the meter turned on. There isn't a lot of room to "increase the price".

There has been some occasions where the meter wasn't on initially. I don't close the passenger door until the driver turns the meter on. If the driver pretends not to understand - I just wave the valet over to explain the situation to the driver. For trips in the city, if I've been overcharged, the amount hasn't been noticeable as my outbound/return fares were similar.

Now there has been a couple of occasions where the meter for a trip to the airport was high by about 40-50bht. But it all nets out the same, as I just don't tip. The driver went to the effort of rigging the meter for no material benefit....