Shorty, you know they are watching us, don't you?
I buy mine from Amazon too - but I try to get ones that are highly rated. Glen, this is perhaps a bit unlikely of a suggestion, but if you know anyone who flies electric-powered model airplanes or helicopters, a lot of the RC chargers can cycle batteries and will give stats on them. When I buy batteries, I stick them on my RC charger (with banana plugs and a bit of creativity to get the contacts to line up) and measure them and I have to say that most of the time, the capacity matches with the advertising.
The ones to watch out for is someone who sells a battery that is exactly the same dimensions as another battery but that person claims >10% higher capacity for theirs. Lithium polymer batteries can vary in capacity per volume, but usually not by that much so I just figure they are fudging the numbers to get more sales.
Also I think there's some truth the idea that batteries take a couple of cycles to "break in". I have no idea why this happens, but I also think it's worth giving it a week or so to see if things get better.