My answer is always "I can review your old documents, but it'll be cheaper to have me prepare new ones." At first people are surprised to hear this, but when I share the following explanation, they understand.
Another attorney on a listserv (whose name escapes me, or I'd give credit) used a wonderful analogy to describe the issue. When you watch a basketball game and the ball goes out of bounds, how does the referee decide who gets the ball? Easy: he looks to see who touched it last. Whoever touched it last is the one at fault when the ball goes out.
As I explain to my clients, it's a similar process when an estate plan goes south and the family is looking to see who's to blame and, perhaps, sue for malpractice. Which attorney touched it last?
In order for me, as someone who didn't draft the will, to be willing to "touch it last" if something goes wrong, I need to have a thorough understanding of the client's needs, goals, and circumstances. This understanding comes from the client's answers to my estate planning worksheet and the information I learn in our initial meeting, which is generally at least an hour. Only after doing so could my review of the existing documents be relevant.
And it's not enough just to look at the major will provisions; I'll need to review the whole document to make sure everything is in order. Since it may not be based on the same template I used, such a review would be quite lengthy as I'd have to go through a checklist to ensure nothing was omitted or added or materially different from the forms I use. Then, I'd need to gather information about the will signing conference to ensure that the formalities of execution were complied with. And if the original documents were executed in a different state? Well, now I'd have to research sufficiently to be certain the documents complied with the laws of that state at that time, as well as ensure that the documents were still appropriate to Texas.
Needless to say, in far less time than it would take me to do that, I could just take the information I'd gathered from our meeting and prepare new documents. I have no problem putting my name on documents I've prepared using this process.
One important exception to this: I am happy to offer a complimentary brief annual "check-up" for my past estate planning clients to determine if any changes of import have occurred since we prepared your documents. Since I can start with the knowledge that your documents were appropriate to your then-current circumstances when created it's just a matter of determining whether any changes to your circumstances or wishes or to the law necessitates a change.
Bottom line: there's a minimum level of due diligence I have to undertake before I'm willing to "own" that document. Most of the cost of an estate plan isn't really for the actual preparation of the documents, it's for the due diligence process and the knowledge and skill to translate the information gathered into documents that meet the need. Take that away, and we're just a document preparation service.