If they start buying sweet Potato’s won’t it be more expensive for the commoners

That's what I was just thinking.

there's pros and cons to everything in this aspect this is the con and the pro is that due to the demand from nobles there will be a need to employ people aka commoners

Or get sweets potatoes polish with not rots stuck out and unpolished ones for commoner there no different in taste though just my idea

Exactly what I thought!