I am fairly new to selling on eBay but I try to do a bit of research prior to listing items. I have a couple of items listed at the moment and I have just checked out similar listings of other sellers. I would have thought eBay disregards apostrophes in a keyword search, but apparently not!
One of my items is a Women's Cycling Jersey:
Results of a title search for Women's Jersey in Cycling category = 11
Results of a title search for Womens Jersey in same category = 55
Any listings with Women's in the title appears in both searches but not the other way around. That means that the sellers who have listed their items using the keyword of Womens are missing out in some searches.
The same applies for plurals. Assuming that most people don't search using Advanced Search, eBay doesn't default search for part of a word.
For example, Bananagrams. There are currently no other listings on eBay AU so I have looked at International listings to get a comparison:
Results of title search for Bananagrams = 74
Results of title search for Bananagram = 18