My own techniques
I go to very few presentations any more. I value my vacation time and generally avoid the presentations. But here are some things that have worked well in the past. My "average presentation" duration is usually an hour or less. The record was about 1/2 hour. They are cut short by the salesperson. The longest was 125 minutes (Diamond).
1. Tell the sales person up front that you have no intention of buying and that you are there primarily for the gift. I will tell the sales person that I know and respect that they work on commission and that I would not like to see them waste too much time with me if they have other prospects available.
2. Print out the completed (sold) sales from eBay for the exact timeshare that you are looking at. Circle several that are under $100. If the salesman is sharp, he'll tell you that there are all sorts of drawbacks in buying resale, like you can't reserve decent dates. But just tell him that you have no intention of staying at a Westgate anyway and that you are just looking for a trader on Interval International. I sometimes tell them of my own experience buying timeshares off of ebay for a few hundred bucks each and that they are working out swimmingly well. But I don't think that you own any timeshares, so you may not want to try this. This has worked several times. Another tactic is to ask politely but with enough volume that other buyers might hear you: "why would I buy a timeshare from you for 10's of thousands of dollars when I can buy off of ebay or redweek for pennies on the dollar?"
3. When the guy asks you how many days of vacation you take (or want to take) a year and how much you spend. Tell him that you typically take 2 or 3 days every 2 or 3 years, that your last vacation was 5 years ago, etc. Also tell him/her that you usually are quite happy staying in a $75 a night hotel. Tell him that your job, family duties, finances, interests, etc. doesn't let you take any more vacation and that you are fine with that. This really messes up their calculations enormously. :hysterical:
4. Before I start a presentation I like to take some control of the time frame. I ask the salesman how long the presentation will be. Usually they say 90 or 120 minutes. Then I tell them that I will honor that time limit and that I expect them to do respect that time limit also. I tell them in advance that if they get within 5 or 10 minutes of the time limit that I will remind them at that point and I politely tell them that I will leave promptly at the time limit and expect my "gift". No games please.

Then I ask them to confirm that they understand what we're agreeing upon. Sometimes if they push back, I've told them that that I need to get out before X o'clock because of another appointment or planned activity.
These salesmen/women are professionals in psychologically manipulating people into buying a timeshare that may not make any sense for them financially and that the prospective buyer perhaps cannot even afford. They'll say absolutely anything (lies, lies and more lies) just to make a sale. So be careful that you don't agree to buying.
If you do buy, make 100% sure that you get the necessary paperwork to rescind after the sale.