I have a friend that has been in the car business all his life, from working the lots to managing dealerships to owning his own dealership.
When we go car shopping he knows the price the car should be at, you look at it and if it is reasonably sound you offer what it should be sold for, and be prepared to walk away if they won't meet that price.
If it is at a dealership it is always 15%-20% higher than that and then they will want "documentation fees" and all that sort of stuff on top.
He never buys used from a dealer, unless it is new and then he gets the wholesale price plus $500 from the fleet manager.
I have never used CarCostCanada but I did buy from a guy who had a dealer license but just worked out of an office and bought the cars wholesale and charged you $500. That worked out for me just dandy.
There is also the option of going to the US to buy your vehicle, I saved $6000 over the best price I could get in Canada a few years back. Easy to import and about $100 for certification.