Lots of domainers make the mistake of thinking their relationship with an end user is over after just one sale. I disagree.
In my opinion, taking things one step further is the best approach. After the sale is finalized, I’d recommend always keeping your eyes open for other domains the end user in question might like.
In other words: you already have a relationship with an end user, so why limit yourself to just that initial sale?
Now sure, some end users will probably only end up buying one domain from you and that’s it. Most, in fact. However, in certain cases, I’m sure interesting opportunities will arise down the road.
Maybe a domain related to his or her niche will be brought to your attention in the future and in that case, the fact that you already have a possible buyer in mind can represent an additional argument in favor of buying that domain.
I’m not saying it should represent the only one because again, maybe the end user in question only wanted the initial domain. What I’m saying is the fact that your existing relationship with end users can end up ultimately leading to new sales under the right circumstances.
Now depending on how many domains you own and on how many inquiries/sales your portfolio generates, this approach can range from being easy to requiring a bit of work. Still, even if you own lots and lots of domains, keeping track of who bought what shouldn’t be all that complicated.
I’d say this can be an interesting addition to your toolkit.
It isn’t an amazingly powerful or innovative approach by any means, just something that could ultimately help you sell a few more domains