Thank you all for your responses and suggestions.

As I said, I have no problems with majority of my transactions.  It's only the very few, picky customers that cause issues.

During my final inspection, if I find the rings are not turning quite right, I either re-service or if I feel it's just out of tolerance level, I'll make note of it in my listing.

On one recent transaction, I accepted a return from an EU country and it cost me nearly 75 AUD in freight costs, 18 AUD to send and neary 55 AUD for return (both Standard Registered Airmail).  It's very hard to recover that sort of loss wnen working on very low profit margin.

My main point is, "What's normal?" and who decides it?

Well, it seems the buyer always has the final say no matter what.