With the projects you have listed, carpet would be the least of my worries. You certainly want to get what you pay for, but I wouldnt be worried in the least of having say home depot install it. But you have to wonder how they can charge under $100 for a whole house install. Most crews I know who do a whole house have a minimum of 2 guys. Between labor, extras, insurance gas ect... $100 nowhere near covers it. So that must lead you to conclude that they are making their actual install only on the backend of selling the carpet. So they overcharged you for carpet and then tried to swindle you into thinking your getting a helluva a deal on install. Or they knew going into it what it should cost and reconfigured the cost so it balances itself in the end but hope your to dumb to see it. I dont see it as though they are trying to rip their customers off necessarily but just using a marketting gimmick. I am guilty of this as well. So now it comes down to overall cost. For me this is what most of my decision making is based on anyways. I guess you run the risk of getting a shotty contractor anywhere, so you go with who has experience or based your decision on recommendations. A carpet guy usually gets discounts from a wholesaler, not a retailer. You save money with wholesalers usually. Its for that reason I typically use subs that are referred to me and then I either get myself a wholesalers account with the company I work out a deal with the get my customers the best deal or I allow/expect my subs to have this agreement with the wholesaler to ensure my customers get the best deal I can provide.