I find that Beck is generally pretty reliable, but they seem to be totally unmonitored when it comes to breaking taxi rules. For example, they always want to know where you're going before you get in the car so if it's not far enough they can come up with some excuse not to take you.
Case in point last night outside the ACC after the Leafs game. Driver standing outside his car says he's waiting for someone, but then proceeds to ask where my colleague is going. I say Yonge and York Mills and suddenly he can get a ride with that driver. Obviously if he'd said Bay and Dundas the driver would still be waiting for that other phantom person. The key is to get in the cab before you tell them where you are going (although this wouldn't have worked in the ACC situation).
I also find they get pissed off when you want to pay with a credit card. I find the solution to that is not to tell them how you're going to pay until you get there. Then they have no choice in the matter.
The point is they are not allowed to turn down a fare and I shouldn't have to resort to these tactics.