I would provide the Serial # to those who ASK ... never reveal it within the auction text. However, I'm not quite sure what this buyer plans to achieve by giving the information to eLuxury?!
One of the BIGGEST scams out in eBay-land, is this whole concept of "you (the buyer) must provide a WRITTEN letter from the [Bag-Maker] indicating that it IS NOT authentic ...". This is totally bogus!!
First of all, L/V, Fendi, Balenciaga, etc. DO NOT "authenticate" or provide any such thing!!! These scammers know it, and so they use this to their advantage to ruse unsuspecting people. The onus is on the SELLER to provide authenticity - NOT the buyer!
In regards to the receipt, I'm often asked "do you have the original receipt?". Again, even if I do (which many times I don't because I may have bought the item overseas), what difference does it make?!?!? The scammers have become VERY good at creating fake receipts - so what does that prove? If you do provide the receipt - make sure that you BLACK out every bit of personal information!!!
Good luck SULI!!