I see that some sellers have their bills graded.
Do you think that helps them to sell at a premium that recovers the cost of the grading?
IMO:
I do believe most people who sell on ebay are expecting to recover the cost of grading and that is why they tend to try to sell their notes at a premium. Whether they actually sell or not is another story. As mmars suggests- higher grades will probably sell for more than a raw note (& are probably more likely to sell).
As for your topic question: Do graded bills sell for more?
I think it depends on the note, its eye appeal/grade, do the collectors have faith in the grade, & how it is being listed:
A) is it rare or sought after? (ie: is there enough interest in the note auctioned?) Devil Faces aren't really that rare but they're sought after & I've noticed more action for the TPG higher grades. If you are talking about BIRD or Journey notes then I would definitely hold off as they seem to be quite commonly graded and typically listed for catalogue (or less) and they (esp insert/replacements) don't seem to be selling that well. I've seen both RAW and graded later series notes that have been re-listed over and over with no takers.
B) if it is sought after and has very nice eye appeal?
If it is an older series and has been graded "original" then it would ultimately appeal to a wider range of collectors who buy online (if there is ONE compelling argument for buying graded notes- it would have to be that there is a 3rd party certification claiming it is original which alleviates a good deal of skepticism amongst collectors who do buy online, and who cannot inspect the note in person)
C) Who/what 3rd party grading company has graded/slabbed the note? (are they conservative or liberal in their grade?)
Although I'm not partial to slabbed notes- I would lean to Canadian BCS rather than the American PMG. However, I have bought the latter (PMG) once simply because I liked the note and the price.
D) How is the note listed?
Personally I believe true auctions garner much more attention, excitement & interest since there is no set (often inflated) starting price & such true auctions test what the present market will bear for a note. However, sometimes I have noticed graded notes very reasonably priced at a fairly low start so I almost wonder if people just search for true auction notes (either way- its a dicey call to go to the bother of grading a note and then have it sell for less then you want!)
If you are contemplating grading all your excess notes so you can sell them for more- I would caution you against it (unless you can get them batch graded for a discount) or you can defer selling now and wait till the market heats up. For one, I would only grade notes you have confidence there will be immediate interest in them now (they are sought after or somewhat rare). IF the are EF or fairly common- I would sell them raw.