Sinistar, just a normal license agreement. They are always there hidden. Probably am too acostumed to legal stuff and formalities.
You feel is to hard? Feel free to comment, and so we could invent license terms for this lines of products. Usually my business software is accompanied by this documents. If not, the purchaser can claim legally that he has purchased the whole product and has even right to ask you for source code! Always set terms. That is the law.
My professional advise would be for any software/middleware developer, to put its conditions on print (or software document) in order to protect their investment.
I had experiences before, and with that experiences was decided years ago to put clear terms.
When you dig into copyright and intellectual property laws, you can see that there should be always clear rules for the buyers of your products, what is they are purchasing and what they are not.
In the case of free products, some are clearly not for others profit making. If the user has intentions to profit, it is rightful to make a deal.
In the case of paid products, there should always be rules, but in this case the person did already purchased some rights to use and paid an amount. Anyway, what did he purchased? You have to tell what your product is.
May the 3d force B with U