Well, in all honesty, at least the salesman would have had the chance to assess the parameters somewhat. I will forever be indebted to a salesman who refused to sell me a power unit! I was very green, and had ordered one locally from a general tool store, which didn't turn up. Good old Yellow Pages ( yeah, that long ago ) turned up a company half an hour away, with them in stock. It was a Kombi unit, to be my first, and I arrived at the dealer, fondled the assorted bits, and said I would buy it.
The salesman asked me what I was going to do with it, and I replied that I was going to make my fortune, cutting grass and hedges all over East Yorkshire. He promptly refused to sell it to me! The thing was, I was looking at the domestic power unit, not the Pro.
I owe that salesman a drink, he was absolutely correct, in this case.