Yes, as with most things in life, you can find reasons to support both possibilities I suppose Jay. Only the seller and / or buyer knows for sure here. It's an interesting scenario to speculate on though, as it touches on a key element of the collecting dream - the finding of something precious for a pittance. That dream being a nightmare of course, if you're the seller.
Jay, indulge me, what do you think was going on here then if you don't think it was genuine? What does a seller of some 20 years with 100% feedback x 1141 have to gain from faking a sale of this book at £40?