I applaud wholeheartedly the work you put in for your charity auctions, and genuinely wish you well with this auction and any more you organise in future.
I really can't stress that enough before I offer my opinion, which you have tacitly invited by posting this in a public forum.
Most people here respect the rules about commenting on authenticity, but IMHO your original post strayed some way from the spirit in which a twelve-year-old boy or girl shows off their TTM from a Huge Hollywood Film Star believing it to be genuine; I would argue that it headed quite a long way towards using the forum as promotion for your auction (which being for a good cause I don't personally have any issues with that either).
I am trying to think of a tactful way of saying that asking people to bid on something which you have even the vaguest suspicion may not be genuine, and have in your posts above actively discouraged opinions being given on authenticity by people you know to understand what they are talking about, could be seen as throwing yourself open to all sorts of bother.
I found this article on The Guardian website
http://www.guardian.co.uk/uk/2008/feb/1 ... .celebrity
and I believe that the law applies regardless of whether or not you as the seller donate the final proceeds to charity.
Furthermore, if I were associated in any managerial capacity with the venue where you are holding your auction and read some of the comments you've made above, I think that I would definitely have some quite firm views on whether or not I wished my premises to be used to sell items over which the seller appeared to openly deny any responsibility for verifying their authenticity.
I'm sorry if this post causes offence, it is not intended to do so.