The pen is mightier than the sword on eBay

You know what is really rare these days, and only getting rarer?

Pen

That's right: actual genuine bona fide honest to God handwriting - it's rare. Once upon a time, back in olden days, people actually wrote letters, took notes in class by hand, hell they used to even keep their checkbook in order - with a pen. But no longer.

So, if you really want to get your customers' attention - why not write "Thanks!" in pen, on an actual piece of paper, someplace in the package you send them.

I guarantee you - it will shock the hell out of them - they'll remember you, and they'll think you're awesome because you took the time to care.