it's not ideal, but I used a silver sharpie to cover my engraving up. the buyer was ok with it because i posted pictures and it looked pretty great - you could barely tell the sharpie was there. and I included the sharpie for any necessary future touch-ups. this is honestly probably your best bet to hide it.
You could get a low cost wraparound cover. Then the engraving wouldn't be visible.
How to Sell Your Old iPad http://tinyurl.com/85d69lk
Other sources to sell.
eBay Instant Sell http://instantsale.ebay.com/?search=ipad
Sell and Recycle Used Electronics - Gazelle http://www.gazelle.com/
For instant gratification in selling a used iPhone or iPad, Gazelle’s Gadget Trader, an iOS app, is tough to beat. In seconds it detects the device and reveals how much it is worth in good condition. Tap the Sell This Phone to Gazelle button and the deed is done.
Sell Electronics for Cash - Next Worth http://www.nextworth.com/
Buy My Tronics http://www.buymytronics.com/
Sell Your iPad http://www.sellyourmac.com/mac-product-guides/ipad.html