How are the roles of tipping and personal lines of credit similar and different in the modern day compared to their roles in the south in the US during the time of slavery?

I recently went on a tour of a plantation in the south that educated attendees about the history of slavery which was pretty eye opening. A couple of the interesting comments made were that:

• Some skilled slaves (e.g. blacksmiths) would sometimes be "loaned" out to other plantations where they could earn tips.
• On one particular plantation, after slavery was abolished and up to ~1960 there was an on-site store where workers would buy goods using credit from future wages. This was a means by which these "free" workers were prevented from leaving as, although they were paid, they were constantly taking on debt from their living expenses.

Both of these phenomena of tipping and individuals purchasing goods using credit are pretty foreign concepts to me as someone who grew up outside of the US. While these conditions were probably improvements to the baseline conditions of slavery, they also weren't as kind as they couldve been, and seem to still be systems that were intended to keep these people subjugated. These are also systems that continue to be used to take advantage of some of the most disadvantaged people in the US today.