Determining your saturation rate:
First what I would look at is the first page of results searching your listing genre. in the case of the OP it is flip flops.. when I searched flip flops the amount of results were 15,574.. the OP had 11 listings in her store at the time. To determine here market saturation I used a nifty "free" online percentage calculator
http://www.math.com/students/calculators/source/3percent.htmanother more simple way to look at it, is dividing the search results by your listings.
For example say I look up blue shoes, and 400 listings show up in the search results show up.. if I had 2 pair, I would have 1 blue shoe listing for every 200 blue shoe listings on the site when I performed the search.
I know learning your saturation rate is very sobering, I really am not trying to discourage you, but make you a bit wiser about the way you tag and title.. which is what I will address next