If you are receiving offers from sellers, that is primarily based on items you have recently looked at, added to a cart or added to a watch list. If you do not want to receive such offers, there is a setting in your Communication Preferences that you can uncheck.
Sellers have no idea that you have already made a purchase or what you have paid, they just know that someone is eligible to receive an offer after looking at one of their items.
If you are receiving emails about similar items, that may be the result of having a saved search with "email alerts" enabled. You can disable those email alerts, or, if you do not intend to buy another, unsave the search.
eBay does not really know whether you intend to buy another of whatever it is you have bought.
