I will throw my 2 cents in, although I suspect there are those will not agree with me on this...I think that if you made it and you want to sell it, knock yourself out. I posted a card in a forum here about 6 months ago and a month later saw (pretty much) the exact same card on Ebay for sale. At first I thought "AGH, they stole my card!" and then I figured, you know what? I could have sold mine on Ebay but chose not to...this person took it and ran with it. The only reason I was upset was because I thought to myself "Gosh, if someone I know sees this for sale on Ebay, they might think that I bought it off of here and stamped my name on the back!" But then I thought some more and figured, eh, oh well...my friends know that I make my own cards so, oh well. I mean, seriously, what would I expect them to do? Write on the back "this card idea was taken from CraftyMel2"? Heck no! I am sure there are others out there who have made similar cards and, who knows, maybe they saw mine and said "Hmph, that was MY card FIRST!". Please.
Ask yourself, "When Iím on my deathbed, will I be glad I was so serious about _______?" Let down your hair and stop being so darn important for a while.