Paying for quotes on repairs/construction project?

I have heard of paying for a house call for appliance repairman to tell you whats wrong. And when you take your car in, you pay to find out whats wrong cause they have to do labor to take your car apart.

But today we had a deck builder call us back and say its twenty bucks to get a quote from them on building a deck. We usually just get three quotes and pick the person with best price but also who seems the most competent. We passed on their services. They did say you'd get the twenty off if they did the job.
I guess it must be related to how expensive gas is and they drive trucks usually with bad gas mileage.

We priced out doing brick pavers which turned out to be too expensive so we had just decided to have DH build a deck when he hurt his shoulder. So if we want something done before winter most likely we will need to have someone else do it..