Be aware that if you do a time share presentation, they usually will not book it on the first day or last full day of your trip. Marriott always seems to book mine at 2pm, essentially ruining a full day. If you only have a 3 or 4 day trip, this may prove to be inconvenient for you.

(And yes, their pitch can be very enticing. Just keep reminding yourself how much the yearly maintenance is, how much the initial cost works out to over the years, and how many Marriott miles you already have that have/will translate into free hotel stays.)