When a sales man tells me I need this and that because the pieces they want to sell me are wearing out I ask them how long they will last and then waste their time with waffling. They don't like to waste time so unless it really is necessary they usually drop it. If they say it will only last a month I tell them fine I will be back then.
I have one advantage. I have a vast mechanical knowledge. Still I get stressed dealing with these types of people. I avoid the big city and pay a bit more to buy local where they know me.
As for my car, I used to work where I get my work done. They don't mess me around.
Did you know commission sales people don't lose their commission on returns. Of course they will sell you something you don't need. Besides are you going to take it back. Here the nearest big city is 50 dollars worth of gas away, add my time and wear on my car and I can afford to pay more local. I realize in a big city you have less chance of building relations with the people you deal with.
My brother uses the same tire store even though they damage the bead on his tires and never get the balance right just because they are fast. I used to redo his tires after hours when I worked for Kal Tire. I had a key to the shop for call outs.
Knowledge is still the best preventive for being taken advantage of. Know what you want and don't settle for anything else. Or at least know how much compromise you will accept.
I also tend to be assertive in my dealings without being rude.
Davit.