It is similar to what went on with gas prices. Until they were mandated to post them on signs visible from the street, you had to drive up to the pump to compare. Look at all the gas wasted searching.
In a similar manner, vendors usually will tell you if you call, but it is awkward to ask the pay rate then hang up if it is too low. Then you have to form a personal matrix of the wages verses the cost of the local area. They want to make it hard so you just take the first one that accepts you.