You know, I had thought about that awhile back before I bought my truck. I have about 10 mopeds (actual mopeds, the ones that you can pedal). First problem, if you are talking about the real mopeds, is that they are not reliable, ever. Carbs get clogged, things rattle loose, belts wear quickly, etc etc. 5,000 miles on one of them is like 200,000 on an automobile. Second, depending on the model, they just don't have the power to pull anything. You can get lucky and get a three wheeled one with double engines (i've seen a few for sale over the years).