First, ask that question before the appointment. Find out if the seller will be speaking w/ other agents, and what their time frame is for making a decision, putting the property on the market, and target date for moving. Knowing this info from a phone conversation will help you prepare a better listing presentation that will address their wants and needs.
I ask a few questions about who and why they are also planning to meet with. There is information in that dialog that will also indicate the seller priorities and goals. i.e. We are meeting w/ John because he is cousin. We are meeting w/ Jack because we saw his videos online and were impressed.
Ask to be the last interviewed. If you are not last, and the seller does not want to sign until they conclude all interviews, ask for an oppty to speak w/ them by phone after they have met w/ everyone to answer any final questions and find out when the final interview is. While I ask to be last, I send the seller a guideline of questions to ask Realtors before listing. My list is far from the typical shop-worn list I have seen circulated for years. My list focuses on things like, "Show me one of your lisings as it appears on Trulia and Realtor.com." with subquestions for the seller to evaluae about the pictures, copy, placement, preferred positioning, etc.
If the seller sets out on a path to interview 3 agents and then decide, it wil often be difficult to get the seller to sign before concluding the process. If the othe interviews are not yet scheduled, you can do a great presentation which might disuade the seller from the need for additional interviews. If they are scheduled, persistent follow up and detail are a better approach than a hard close.
I am not a person who is afraid of a hard close. I can ramble....but I can also deliver strong closing statements, and remain silent without any difficulty. I don't use hard and strong closes in an attempt to disuade other interviews, but I will use an assertive close to help narrow choices, confront objections, and make a decision. If a seller is undecided and afraid to make a wrong decision, helping them understand what you will or can do is the right thing. Use a more assertive style of closing. If the seller is committed to their process of interviewing other potential Realtors, respect that. Use follow up skills.
Some Realtors offer a no questions asked termination of lisitng agreement as a closing tool.