Okay, well here is my thoughts:
If you want to keep a pattern exclusively for your own use to make and sell the item, then do not sell the pattern.
Once you sell the pattern, I do not care what instructions you have on it about copyright, for personal use only, etc., you have lost control once you sell it.
Here is the best example I can think of:
An Etsy shop owner has a particular pattern for sale for a hat, but states it is for personal use only and you cannot sell items made from her pattern. A little while later there are 12+ pages of that same hat for sale and people are also selling a pattern for it.
How are you supposed to stop that from happening? I hardly think it would be worth getting a lawyer to chase down the offending sellers. Imagine the legal fees.
And just one more thought...what do you do about people who can just look at a picture and copy the item just by looking at the picture?