As a business owner, I am going to donate (1) to get positive exposure for my company in front of potential customers, and (2) for the tax deduction.
You need to be able to tell me in marketing terms who will be at your auction (how many people, their demographics, etc.) and yes, give me a sense of what other types of donations mine will be competing with/beside. If there was an auction last year, let me know how many people came, and show me a list of typical donations by category and their average bid. I don't want to donate a weekend at a flashy resort (value $600) when the next-best donation is a basket of muffins (value $10).
Finally, make it as easy as possible for me to make my donation. I shouldn't have to drop it off -- you should pick it up. Whatever it is.
Good luck!