Lol, you work at an automall and have no clue on the value of the Ecoboost f150? Come on man, ask a salesman, or at least one of the techs, they will know.
Yes, 28k for a truck that usually list for 50k is pretty good. Just make sure and look at it good, no mechanical problems. Its still a fairly new engine, so theres no telling in what could go wrong.
Ford has come a long way though, they are making much better vehicles than they were. My dads F150(5.0, not ecoboost) is a great truck, he hasnt had any problems and hes had it for almost a year now.