Yet another reason my kid rules

So we're out buying tires. First we go to NTB and they give me a written estimate on what they recommend with the alignment it's just over $400.  Then we go to Firestone, who do not carry the tire we have the estimate for, but offer a comparable model.  Their estimate with alignment and extended warranty and an oil change is $490.  Alex hears that and tells me we should go back to NTB because it's cheaper.  The salesman tells my son that their price does not include the warranty or the oil change.  Alex tells the man he's still too expensive by $15 and that's not a very good deal.  He then announces to the 3 staff members and their customers that I work hard for my money and I can't be throwing it away for no reason.  The salesman then explained that the tires he was selling us had 60,000 mile tread life and the other tires had 50,000.  My son said that may be so, but he still thought I should go to NTB.  The sales guy looked at me and asked what *I* wanted to do.  I looked at Alex and said I had to agree with the man of the house.  The guy then took $15 off my alignment and $10 off the oil change.