It's not like there's much of a market for baby Changelings, is there? Who else would be willing to pay anything
for one, much less more than 8 slips?
The Federation might want a baby Changeling for study, but they're not going to pay
Quark for it. They'd just confiscate it.
The Romulans might want it, too, but they'd probably just steal it.
The Klingons would just kill it.
The Cardassians might actually pay for it, but would even Quark want to deal with them at that time?
No, I think 8 slips was probably a good deal for both parties involved.