That’s the thing though. I think people talk about “silly Ferengi crap” and while obviously they are intended as a sort of parody of American capitalism and all that, they are a ruthlessly logical species and culture.

I think the Klingons tolerated Quark because the situation was so strange, and Quark exploited the Klingon’s system of honor. The Klingons were shellshocked from the idea of a Klingon woman marrying a Ferengi to take over her house. I think they were genuinely a bit curious to see how a Ferengi would respect their rules, and it seems Quark demonstrated an adequate understanding of how their honor worked (even though he didn’t agree at all with it) for them to give him a chance. He used two trait which any good entrepreneur would have: the ability to take risky moves, and good social awareness.