Custom Card Printing

[teesaw]

I found a site online (which I am not linking to, because this post is not some spammy, back-handed advertisement) that is running a cyber monday sale on printing custom playing cards, and 108-card decks are $6.50 + $7 shipping (works out to just more than 2/$20 with tax and such). 

I know there is access to high-res images for some of the fan-made decks online, but I'm wondering what the customary rule is regarding self-printing.  I know that someone (or a group of people) worked hard to put these decks together, and I certainly don't wish to try to take away from their hard work, or get something for nothing, which is why I'm asking. 

What's the general rule here?

[breadmaster]

I'm not sure there IS a general rule. 

I guess as a courtesy, get the go-ahead from whoever created the cards.

legally, i'm guessing there's no obligation