Sort your search results by price descending and the ones at the top are the end user sales
Other than that, the venue the domain sold at will sometimes give you an idea.
If you see Domain Name Sales, Most Wanted Domains, BuyDomains, Afternic, Media Options, Nokta, and Private it is almost always an end user sale. Sedo is more often than not an end user sale. GoDaddy is a good mix but I would generally classify it as wholesale. NameJet and SnapNames are much more likely to be wholesale. Pheenix and DropCatch are rare to find an end user.
For the venues that sometimes get end user bidders like NameJet, I would still call it wholesale pricing even if an end user won the domain. They’re only paying one bid increment above what a domainer would pay after all. Then again, if two domainers get in a bidding war they could easily drive it up into or above the retail range. So venue alone won't always tell you.
All that said, I don’t think there is really that clear cut of a distinction between wholesale and retail prices given how subjective domain pricing is and how high domainers are bidding lately. If you ask several experienced domainers what they think the wholesale and retail price of a domain is you’ll get a wide range of answers. Watch the DomainSherpa.com Review show where they have the Name That Price game to see it in action.
A domain in my hands is worth less than if it were owned by Mike Berkens or Frank Schilling because they have the means to say no to high offers so they can shoot for really high offers. They’re also playing a numbers game that people with small portfolios of average quality domains can’t play. Quote prices based on comparable sales by Berkens and Schilling and you’ll probably never make a sale and wash out of the industry.
If a small or medium sized business inquires on a domain you might quote one price, but if a Fortune 500 company inquires on the same domain it is suddenly worth more even though none of the stats or comps changed. Pricing a domain is more of an art than a science, it may even be more about the parties involved than it is about the domain itself, and there is no right answer that a tool can help you get to.
Back to the original question, I would say there are really high sales that are obviously retail, there are really low sales that are obviously wholesale, and everything in between (most sales) is hard to say. If you're trying to price for an end user, you're always going to want to sort by price descending and go down until you find domains that are actually similar to yours and justifiable as comps.