Or even better, listen and keep saying no. Pay attention to what the offer/offers are so if you really want to do one, buy it on the timeshare resale market. They go for as low as $1. Make sure the points are transferable, as I know with SPG, not all the properties allow transfer of the points, only the week, which makes it complicated.
I should point out that these are rather painless, and the rewards are decent: did a 2 nt stay at the Wyndham Grand in Chicago at basically 25% the cost of the regular room rates; the "have a night on us" was used at a Wingate in St Augustine covering almost 90% of the cost of the 2 nts there, they sent the check promptly, and got the gift card at after the presentation. All totaled, made a few bucks on the deal and got 4 nights credit towards Gold status. (Not that that is worth anything.)