While it is entirely possible that the panel is overrated, keep in mind that there are many factors at play when it comes to the output from a PV panel.
First of all, they are rated under IDEAL conditions, which you will almost never get. The solar irradiance/potential in your geographical area, weather and smog conditions, time of day, and angle of the solar panel toward the sun, will all affect the maximum output you can get from it, and in most cases that is going to be somewhat less than the maximum rating. So you always want to size your solar panels a bit larger than your energy requirement.
In this case, I would say the panel is very likely overrated. It's physically very small and has an even smaller effective surface area as the individual PV cells occupy only a small amount of the total area! I don't see how you could ever get 1W out of that.
Rough math:
Panel dimensions 132mm x 63mm, total surface area 0.008316 m2
Based on the pictures, I'm estimating only about 40% of that is effective area (actual PV cells): 0.0033264 m2
1 watt / 0.0033264 m2 = 300.625301 watts per square meter
The sun energy reaching the earth: 1360 watts per square meter, only about 70% of this or about 952 W/m2 actually reaches the surface, at most.
That would make your panel theoretically 31.5% efficient in order to produce 1W of power. Even the best of the best solar panels money can buy nowadays, are about 21-23% efficient.
So yes, I'd say that eBay panel is greatly overrated.