or almost anything else.
Other things being equal, Economy of Scale says a larger trimmer (7A) should cost less per amp than a smaller trimmer (4A).
But with the six trimmers I looked at from either Sears or HD, with the smaller I'm paying $7.50 per amp, with the larger it's $9.30/A.
For $30 I could get either 4A or 4.2A so it would have been the 4.2A but I didn't want to go that cheap.
The average is $8/A and I paid $50 for 6.5A.
Possibly both stores within walking distance of each other have their customers believing that more money = better.
And who's going to draw a graph to make more sense of the prices and features?