I have to agree with Andrew, but then I sell a few when I have them every second year or so! Mind you at $13 a throw - I aint making diddly profit, but it allows me to buy some new bit of brewing kit. This year my profits will go towards a new kettle. I think the question is - what is reasonable?
I like to keep it nominal, and relative to what our northern hemisphere brethren pay at, for instance, freshhops or northern brewer - around US$8-9. I think that is a bargain price and a modest return for your efforts.
Having said that, you are well within you rights to personally feel jipped if someone is flogging off what you gave in good faith though. But, so what. The value of anything is what people WANT to pay. That is a free market I suppose.
It may be poor form, but then, some might also say that owning a online brew store and being really active in brewing forums is also a bit dodgy. Me, I dont care, and why should you, as we are operating as a supportive community overall, full stop.
The charlatans stand out like dogs balls and in the end disappear because the community finds them out and refuse to deal with them. The Karma Brewbus will always hunt you down sooner or later.
Anyway, enough from me.