Sometimes we can find "fill in the blanks" types of contracts and its easy to complete and other times people try to create a contract themselves, and it doesnt turn out so good. There are some sloppy contracts out there and you dont want yours to be one of them. If you have experience creating and filling out contracts and you also have experience in counter offers then maybe you can safely create a contract for yourself and your client, but, however, if you are new to the task it may be a good idea to get the assistance of an experienced lawyer or agent.
There are many unforeseeable mistakes that can result from writing contracts when you dont have the experience or expertise to be doing so. If you keep in mind the best interest of your client it should help you make these types of decisions. Sometimes it may be easier to just fill it out on your own, but again, keep in mind you are working to help another, and what youre doing may not be helping them.
Also, another point to discuss is verbal contracts. These used to be the way things were done in the old days, but today is not the old days. The new days require that everything be in writing, its just a good guideline to follow. In a world where everyone is suing everyone else, keeping everything in writing keeps everyone out of trouble. Just cover your hind side when dealing with contracts.