In Start and Grow Your Limited Scope Practice: How to Make Money Serving the “Do It Yourself” Client, I lay out numerous reasons why you should consider limited scope representation (also known as “unbundling” or “unbundled legal services”), walk you through the ethical and financial considerations involved in limited scope practice (and most others), and give you plenty of practical advice on setting up, promoting (aka “advertising”) and running a limited scope representation practice. Here is an excerpt from the chapter entitled “Saftey First: 6 Ways to Protect Yourself:”
We start with the recognition that the agreement to hire a lawyer—or for a lawyer to perform legal services—is a contract. The elements of a valid contract, therefore, must be present. The limitation on the scope of a lawyer’s duties and responsibilities must thus be by agreement with the client. The ABA’s position is that the options are very broad as to how much the scope of services can be restricted. The restriction can apply to the type of assistance, the number of matters, the duration of assistance and the terms under which the lawyer is available for other services or an extension of the agreement. It is essential that the client agree to the limited scope of your services.
The limitation must also be reasonable. Reasonableness is subjective and based on the specific situation. Just because your limited scope representation is normally reasonable does not mean it is reasonable in all situations. You will need to make sure the services are appropriate for that client in that specific situation on that particular day. Every time.
 Comment 7, ABA Model Rule 1.2.