First, be aware that the first price that the guy from the TV ad company gives you is at least twice what it will cost if you bargain hard and get competitive quotes.
They are a lot like politicians.
Question: How do you know they are lying?
Answer: Their lips are moving!
Also, the #1 rule for dealing with people who come to your house to sell you something is, "NEVER sign anything during that first visit, and never sign anything that they haven't left with you so you can read it at your leisure". That special first-visit "only today" bargain is ALWAYS available at a better price.
I had a NewPro outfit in my house a year ago, and the first price was $23,000 (more than my house cost when I built it). They NEVER showed me the "guarantee" that it would reduce heating costs by 50% or some such thing. A guarantee that they won't let you review with your lawyer is useless, if it exists at all.
After I let them stew a few days, the manager came out and told me they had a factory that was moving and I could get the windows "Now" for about $11,000.