the proto/beta ferengi in rascals can hardly count, as they got a total revamp after that (not the way they are looking) they just didn't work that way and needed to be re-invented. if they called it rosegarden it would still be slavery (if it was).
i didn't say that. i said it's probably illegal but they don't care as long as nobody gets caught. and these ferengi are criminals who actively rob an alian starship, anyway.
where is ever a statement that she is the posession of either of those? they are responsible for keeping her 'in line' but if she shows remorese and guves back the earnings they're not in trouble. quark can't force her to give back the dosh. if she can have her own free will and bring anybody in trouble for it she's not a slave. if she were a slave quark could give back the cash, case closed. he can't.
you describe indentured servitude correctly but whether brunt says it that way or not what is sold is not the person but the right to exploit said person until the debt is repaid.
none of which makes them slaves
all of them - the big dead (and only that makes somebody a slave) is owning a sentient being.
i will come back to this later today - after i rewatched rules of acquisition slowly.