Exactly.
The point is, at a later date when someone else has put up a sale thread for the same (or a similar item) a tentative buyer might refer to this pricing and starts a debate with the seller claiming "X had previously sold this item for XXX INR sometime back and the pricing is higher on your thread". I'd say, let the seller do all the research prior to putting up his items on sale. Agreed the pricing can be a reference but in cases like these, it has its downsides as well.
I for one always prefer blacking it out to avoid such instances. If it is imposed as a rule to have the pricing on the thread, I don't have problems.