Avot Chapter 1, Mishneh 6

I apologize in advance if this post is written a bit cryptically. I’ve posted my question numerous times and Reddit immediately auto-deletes my posts even though there’s nothing in the post that violates the rules of this sub or of Reddit generally.

So here’s the question:

Mishna Pirkei Avot 1:6 ascribes a particular saying to Yehoshua Ben Perachya. There are 3 parts to the saying. The part that I find troubling is the second part of the saying. What does it mean to acquire/buy a friend? I can think of a lot of ways that people become friends but none of those involve buying or acquiring the friendship.

I’m interested in getting insights from the sub.