Such system shouldn't even exist, but unfortunately it does and people are willing to pay for it.
2 retainers is abit restrictive honestly, I can afford to hire two more and that's enough for me, but why do I have to pay a sub over my sub that just feels abit greedy?
Also bad currency conversion exists, not everyone is living in america/europe.

1 retainer lets you list 20 items, you get 2 retainers, that's 40 items
10 retainers at most can be hired that's 200 items

200 vs 40? Small difference, right?

Inb4 'gil is worthless anyway' arguments. I don't think retainers should come with a market listing limit.