On this point I completely agree with Dan (well, unusual, but can happen...). On the image below the red arrows point at different gilding of the same items in ura and omote. Quite interesting, the green arrow points at an unpressed area (confirming the way of production).
So for sure, IMHO, a sanmai tsuba of lower quality BUT possibly very old (usualy papered as ko-kinko by NBTHK). Not worth the price asked, but not rubbish...