You'll find that one of the biggest problems is that people expect the same from their handmade pieces as they get from the mass-produced stuff they're used to, which has almost inevitably been plated with fine silver rather than being properly polished, and as a result doesn't really start to tarnish until that fine outer layer has worn away (as it inevitably will).

If it's a higher value piece, I'd recommend including a small cleaning cloth (even one cut down from a larger one) and a little explanation that silver will tarnish when in contact with many different things, but that it can be brought back to a high shine with just a tiny bit of effort.