I agree completely with Mike, though my experiences vary.
I have been to many presentations at The Royal Resorts, and only once felt a bit pressured by an over-enthusiastic salesperson (he was new). Their presentations consist of a ride to one of the resorts, brunch or lunch, a walk around the resort and one of the villas, and then they discuss price and availability. The time in the meeting room is not long - maybe 30 minutes if you listen politely and say "no thanks" - and then you can hit the pool or beach. Nonetheless, it's still time out of your vacation.
The Royal Resorts do not have a "menu" of options like some other resorts - the price is fixed (except for some reductions such as 10% off for owners) and there are no amenities to add on or subtract. The contract is standard for everyone, so there are no extras or deletions. Nonetheless, be very aware that resale is almost always less expensive than the original developer prices. Let them know that you know about TUG and eBay, and ask to see what they have available in resales (e.g. owner defaults). Take the prices back to your villa and get online and shop around (eBay, TUG, Redweek etc.)
We occasionally read on TUG of people who have changed their minds right after buying through the Royal Resorts, and have just gone back to the sales person and gotten it cancelled without a hassle.
HOWEVER, I have also been to other presentations - here's what to watch out for:
READ EVERYTHING, take notes, take down names and times and promises. Then go back to your unit and read over all of it. DO NOT agree to anything until a day or so later - trust me, the deal that is "today only" will still be there tomorrow.
DO NOT SIGN any kind of a waiver of your right to cancel within five days. It is not legal for them to ask you to sign, but this practice will make you think that you can't chance your mind, when you absolutely can.
DO NOT SIGN-UP for a presentation or leave a deposit while you are in an airport or public place - you may have trouble getting your money back, and it may not be clear what you are signing up for.
DO NOT BELIEVE any promises that they will sell your existing timeshare(s) for you (usually at a high price) and take that off the cost of the new one. Check online (eBay, TUG, Redweek etc) to find out what your timeshare is worth - probably far far less than they may be promising. If you do sign your timeshare over to them, they will probably NOT sell it, you will probably still be responsible for maintenance fees, and you will not have use of it.
DO NOT BELIEVE promises that they will rent your units at exorbitant rental rates so that you can make money. Depending on the timeshare, if you rent you may well be able to recoup your maintenance fee or even get back double or more (e.g. a beachfront Royal Resort during New Years) but in general you will break even if that.
WATCH OUT for situations where you may be "held captive" - we went on a "free boat ride" and had no way to leave a high pressure presentation (except perhaps to swim).
DO NOT SIGN UP FOR any credit cards - people have returned home only to find a bill from a new card they didn't realize they had.
DON'T DRINK ALCOHOL at a presentation - a few free drinks aren't worth the risk of spending tens of thousands of dollars you might not otherwise have spent.
BE PREPARED with your answers - No thanks, currently unemployed, filing for bankruptcy, cheaper at resale.
HAVE SOME COUNTER-MEASURES handy - wear a TUG t-shirt, bring a crying baby, develop a sudden bad stomach flu.
The best advice, though, is to not go. This is your vacation, and it's usually not worth losing a half-day or a day of it for a sales presentation. Unless the incentive is VERY GOOD (e.g. tix for four to XCaret?) and you know you are good at saying No, just don't go.