Turn ons:
* Excellent design
* Metallic inks or foil on cards, where appropriate
* Good price
* Thin borders or no borders (for many of us, while others of us do prefer borders. But, where there are borders, not very thick)
* Good manufacturers (see JuFiN's list above)
* Good tuckbox with embossing/debossing and/or foil
* Good theme (and, let's lay off steampunk, cthulu, pirates, and skulls for a little while, unless you can *really* blow us away with your design)
* Good art
* Reputable partnerships / fulfillment house a plus.
* Regular updates to the project and engagement in the comments section. Doesn't have to be every day, but "regular."
* Know the "rules" of traditional playing card design (standard suits, indexes, suicide king, which courts face left/right, two-way courts and backs, etc.). If you break a few here and there, that's fine as long as there's a reason that makes sense.
* Big bonus for engagement here at UC in threads that aren't just about your project.
Turn offs:
* The opposites of the above
* Excessive hype in the ad copy ("The most original, unique deck ever made in the history of playing cards!!!")
* Reacting childishly when things don't go according to plan (which is inevitable, at some point)
* Reacting childishly to criticism. Esp. when it's constructive or well-intentioned. Granted, you don't have to like it when someone says, "It sucks," but replying with, "I hate you! I hate you! I hate you!" doesn't show class, either.
* Listing "Founders" as one of your earlier projects.
I'm sure this list isn't exhaustive, but you get the idea.