An unwanted answer is you get what you pay for. A lot of more reliable gunmakes of a somewhat higher price which do not have that stain, of a gunmaker making an incredibly foolish gunsmithing mistake, or if their agents did it, released unregulated rifles.

I would go for a Chapuis, Krieghoff, Merkel, Heym or Verney-Carron or other brand before a Sabatti.

I would consider a Sabatti ONLY after shooting it and see how it shoots.

Or expect the price to be low enough to have it re-regulated.

Unless I just wanted to take a blind chance at it and toss a coin.

It is always the cheapest is not the best choice in most transactions.