A piece signed by Walt Disney is certainly a rare occurrence. If you are truly interested in a piece, then you may need to make up your mind quickly. But not for any other reason. They look great, and really add to the aesthetic value of a piece, but take into account the cel that you are buying. That's where the value of your purchase is.
Same logic applies to a nice frame.
You do have other choices. Wait, look, call other dealers, go on the internet. The market has been blown wide-open in the last few years, use it to your advantage. The above does not apply to really rare, exceptional vintage art. Particularly in regard to the internet auctions, don't just buy a piece because it sounds like a great deal.