Roofing seems to be very price competitive. Many people see all shingle jobs as equal and simply select the lowest price.
Review carefully what is on the quote. If its not written on paper, it was never discussed and never promised. If the quote says "one roofing job, $xxxx.00", throw the quote in the trash. Go online and compare reviews of the suggested shingles. Are they quoting synthetic underlayment or tar paper? Are they going to strip the old shingles, or shingle overtop of the old ? Fair chance they will find some rotted sheathing when they strip off the old shingles --- is the price of any sheathing replacement listed on the quote ? (Estimator can't guess how much sheathing they might have to replace, but it should be listed as $xx per sq ft, or per sheet). Ask if you you currently have sufficient ventilation.
Last time I had my roof done, I chose the most expensive quote.
Also, note that the warranty on the roof mostly isn't worth the paper its written on, so don't put a lot of stock on that. And keep in mind, even if you are going to sell in 20 years, first thing buyer's inspector will check is roof and how much life it has left in it.