So here's a related question for you guys that acquire epubs from different sources.

Have you noticed a significant difference in the quality of the epub source files from the various retailers? Is one of them consistently outputting better quality epub files with better markup than the others? My impression has been Kobo often puts out pretty clean epubs, but I haven't done any kind of thorough comparison or diffing.

I ask only because, it's often not a clear-cut decision between which store I'm going to buy an epub from. Often prices are same or within a buck or two, and all other things being equal, if one store is putting more effort into nicely formatting and structuring the source files, I'll buy from them.