Anyway you don't have much of an option if it's original disks your selling, most Amiga games used custom loaders (ie: not DOS) and so even with something like X-Copy they're going to show up as being full of errors... 
I disagree. Bad blocks tend to show up when using verify, because usually one of them is on the edge beween two values and is read differently when read again. Consequently every disk you can store as an ADF can be checked by this method with nearly any backup program with verify. You improve the odds of discovering errors by copying twice or thrice.
The quesrion is not whether they are (Amiga) DOS formatted, but whether they obey to the standard Amiga track/sector layout, which is true for over 90 percent of my disks, then again I have only very few games and they are all pre 1993.
XCopy is only better in so far, as it will read Disks containing long tracks, etc. The long tracks will be unchecked, but the rest will be fine.
