There's a knock on the door; she answers. Forty-five minutes later she has an estimate to replace all the windows. She's convinced this company is the best. Later that day her family warns her that the company she wants to hire is known for shady practices, such as giving

discounts for leaving a five star review before work even starts. Without her family's knowledge she signs a contract. A few months later she is stuck with a huge bill for cheap windows installed with terrible workmanship. This bill is so large it will take all of her life savings to pay it. Sure, better windows would have been good if she could afford them but she couldn't and they weren't that important. Also, if they really needed to be done, her family could have helped her find a reputable company to do much better work at half the price.
An older couple had some vents not working well. They called an HVAC contractor to check it out. The contractor had them convinced that it was absolutely necessary to replace the whole system and to move the attic access. This would "only" cost $8000. A family member who was a contractor came over and discovered that a couple connections had tape coming off. After fixing those connections with less than a roll of tape, all the vents worked perfectly.
A widower is down to two roofing companies. He settles on the one that is "factory trained." A month has now passed since the job started. The company has left the job unfinished and won't return to complete it. A few months of fighting with the company and he finally decides to call another contractor to finish. The other contractor discovers that a large section of the roof will have to be redone too. This widower is stuck paying to tear off a section of brand new roof and have it redone and then paying to get the roof finally completed.
All of the stories above have a few small details changed but they are all based on stories that happened to my family and/or customers and/or potential customers of mine. There are more similar stories I could tell. Please, be careful when choosing a residential roofing contractor, check ratings and actually read the reviews, look roofing contractors up on the Better Business Bureau, on the Contractor Board's website, and make sure you understand exactly what each roofer is offering. Don't be afraid to ask contractors for proof of insurance and to check their ID against the Contractor Board information before signing a contract. If you have an elderly friend or family member help look out for them because predatory sales people will target them. When you hire a good company, spread the word. Last but not least, do your part to never take advantage of people. Treat everyone as if they were your grandparents.