Membership usually needs to be maintained year after year to avoid paying the Membership Fee again.
The fine print in a typical exchange membership says that they are only obligated to find you a resort in 2 years once you give up use of your resort for exchange. Should they fail to find a resort, you lose your resort and the exchange fee. With ResorTrader you never give up your resort prior to finding a resort for trade and you never give us your resort to control the trade. You are in control. You don't risk losing your unit to an exchange membership company with ResorTrader.