The reason many galleries don't want to handle artists who sell on ebay is that it will undercut their selling prices. It may be a good way to get seen by some galleries, but once you have significant gallery representation, you may well be asked by more than one of them to stop ebay sales because A: every ebay sale means one less print they can sell, B: one less commission they can earn, and C: because it is an auction, it can go for less than they are selling your work for. If you can not only sell work without paying them a commission, but your side sales will undermine their pricing, why would they represent you?