These are some of the Neopets No-no's:

Having a religous/political theme in your guild.

Selling a Neopets, accounts, etc. for Neopoints

Using an autobuyer or a similar program to buy from shops

Using a cheat program to play games

Having Neopets date other Neopets

Performing services(like making layouts or drawing pictures) for other users for Neopoints, items, money or anything else. (you can make things for other people just as long as you don't charge them for it)

Taking someone else's picture that they created and using it for the art gallery or Beauty Contest

These completely cover all of the Do's and Don'ts of Neopets.
Scams http://www.neopets.com/wallofshame.phtml
Terms and Conditions http://www.neopets.com/terms.phtml
Basic Problems & Questions http://www.neopets.com/contact.phtml