My rule of thumb is that the harder the sales pitch is the more likely it's not a good idea to buy.
I used to hold the same view before I put a couple years in at an electronic retail store. Corporate wanted us to push extended warranties, but often we simply offered them when they showed up on the screen, even though selling them would boost our paycheck.
There were just a few products in the store that I actually pushed the warranty on, simply because I knew the store policy would actually be to replace on the spot, or because I knew the product was prone to failure from past returns. In the second instance, the product were uncommon, very difficult to come by, so there weren't any alternatives, even at competitors.
For these products, I viewed the extended warranty as a good plan, so I did made a harder pitch then I normally would, because I knew the chances were high that the customer would end up using the plan, and then coming back to buy something else because they'd realize I was looking out for them. It was really less about the simple sale, and more about not having to deal with angry/upset customers down the line.
The unfortunate part is that for every salesperson out there who is actually trying to look out for the customer (even though it's motivated by self-interest), there's at least ten sales people who either don't know, or do know and don't care. If you find that one that knows what the hell he's talking about and tells it like it is, get his card and name, and stick to him til he moves on to another job (which he will).