Sure. Its all fun and games until they change the saftey word to fluggaenkdechioebolsen. After that things go downhill.
or whistling as a "safeword" for choking.
Anyway at least in case of the Orions we know they have themselves sold (please note the odd sentence structure) so they can control those poor fools who buy them.
At least it was this way in TOS and earlier.
It would appear this was no longer the case in the later shows, at least there was no mention of Orion slaves in the other shows while the Syndicate is mentioned.
So perhaps slaves are only an issue on worlds beyond the Federation's reach...