Some few years ago, back when eBay allowed Sellers to leave negative feedback for Buyers, they based feedback percentages on a Seller's entire sales history; now, it's based on just the last 12 months of sales. That can drastically affect a Seller's feedback and give a slanted view of a true summary.
If a Seller actually changes his account (closes one and opens another), feedback goes with the account. If a Seller simply changes ID name on a continuing account (or merges 2 or more accounts), feedback remains unchanged. There can be a number of legitimate reasons for changing an ID name. I've not changed mine in the 15 years I've had an eBay account, but I know several Sellers that have changed names simply based on a change in item sales emphasis - they merely wanted one to better reflect their new items. On the other hand, some seem to regularly need change as a result of impatience and restlessness.
I don't really see leaving cross feedbacks for oneself over multiple accounts as being very frequent, especially at those prices. EBay charges a 10% fee per sale (including shipping). I suppose, of course, some sellers might feel feedback is worth $3.90 each.
Search parameters can be tailored to a great extent. If you're looking for a specific kit, you probably won't receive a great number of hits. Simply minus out everything you don't want ( -decals -instructions -parts, etc.) and refine it over time in a saved search. If you look for all kits in general, or 'Ford,' 'Chevy,' 'Mustang,' etc., you'll still get hundreds or thousands of hits whether you add general parameters or not. That's only to be expected. For that reason, I always search for specific ranges only.