The old saying " the customer is always right" seems to be forgotten by many customer service staff now. Even if I knew the customer was off track, i always approached a sale with the view of "this is what you want, this is what I can deliver to meet your exact requirement, or what I could supply at a similar cost that mite be better".
7 times out of 10, the customer went with my recommendation.
The key is not to knock the opposition. Respect others in the sales game. The same respect for others as a sales person and knowing what they sell and your point of difference is the main advantage you have. Unfortunately, most main stream salespersons now couldn't give a rats because they could be selling cell phones one month and bull bars the next.
So, as a customer, you need to do your research and build a relationship with businesses you can trust. Research is done via legwork, referrals from those you know, or via contacts built up by meeting like minded others (via myswag for example).
So, the other old adage, "buyer beware" is very relevant. Don't be a "wood duck", ask questions, seek endorsements from others, don't say "yep,yep,yep" at the first quote.
Oh, and stozz, they wouldn't have got past two strikes with me.