When it comes down to the time when you want to sell your beats you must have the proper contracts. Yes, this should be a part of your studio in a folder put away, even if it collects dust. Hey, anything can happen, P. Diddy could come knocking at your door, although Bad Boy Records contracts with their musicians are considered to be sometimes "questionable".
When selling a beat, oral agreements will not hold up in court and if the artist is sued on the basis of copyright infringement, without the paper saying you transferred all rights to the artist, the legal implications would shift to the creator of the beat, which is you. If eyebrows are raised by your unexpected professionalism, just tell your potential buyers that it's nothing personal it's just how you transact your business.
Although you can write the contract yourself, with personal necessities of your liking, it is very much preferred that a lawyer be contacted as you may write things that are too vague such as, "in the case of a lawsuit you don't know me". That is more comedy than business. One such person to write this type of personalized contract for you is a music attorney. While initially expensive it will pay off tremendously if perhaps any legal matter pops up that reflects on you when it doesn't have to. Another point to consider is you only need a couple contracts for selling your beat and then you're set for life and may not ever again talk to that legal money swindler.
There are two main types of transactions that are common between a beat maker and an artist, one that gives "non-exclusive" rights and the other that gives "exclusive" rights. Exclusive rights are usually priced much higher than non-exclusive rights. Make sure the music attorney draws up both these contracts separately.
Non-Exclusive or leased rights to an instrumental are when you sell the artist the instrumental but give limitations and restrictions on how the beat can be used. Non-exclusive rights may prohibit the use of the instrumental for commercial sale or promotion, strictly for mixtape use and also no rights of complete ownership to resell the audio in any way. A con about a non-exclusive deal is that as a sampler you would still be held liable for any copyright infringement and not the buyer of said beat unless stated in the contract.
Exclusive rights would transfer all ownership of the instrumental to the new owner after purchase, so any legal implication would go directly to the artist. In this contract it is also common to demand a number of points from the artist's album on top of the set price of the actual instrumental. A point in music industry standards is equal to 1 percent of the amount of the revenue an album generates. Some beat makers may not charge a set price at all on non-exclusive right, and only points depending on how famous, profitable and consistent the musician's history in music retail is. These are generally the common type of deals made by beat making record producers at successful indie and major record labels.