Triathlon - How do you evaluate a bike?

I have read a lot of the other posts about tri bike recommendations. However, I don't have a real sense of how to evaluate a bike. Do any of you have a routine to help decide which bike is the best for you? Being somewhat of a novice to the sport (this is my second season), I would probably need to ride a bike for several hours over various terrain (rough roads, hills, windy conditions, etc) to get a real feel for it. I doubt the LBS would like me to put that much wear on their tires. And since fit is so important (and time-consuming), do you typically ask the LBS to do a detailed fit for every bike you are considering? Even narrowing the search to 3-4 would be a lot to ask. Any insight or tips on proper "buyer's" etiquette would be greatly appreciated.

Some LBS will let you go on long rides, just ask the owner/manager ahead of time.

Usually for fitting you need to know what rough frame size you need, then they adjust the seat. Then you ride. They don't do much more than that because it takes too much effort. If you already know of a couple models you really like, and are serious, you might be able to have the shop set them up for you ahead of time. It's worth asking.

Some of that might depend on the type of shop. A chain-retailer shop might not be willing to do it, but a local shop that the owner works at might be more helpful.

If you knwo what it is you are looking for(model, ect.) call the shop ahead of time, and ask if you can go for longer ride. Then go out and ride it like you would race it(not like you stole it). That will give you the best feel. Find some nice hills, go up and down, try standing up, try and feel the lateral flex to see if it is neglegable. You just need to find a frame that best suits your need.