Here are some big red flags that this is a scam:
-You got a cold call from them
-They are offering to buy or rent your timeshare for far more than it's worth
-There are upfront fees that you have to pay to sell/rent your timeshare - they may not have disclosed the fees to you yet - they will wait until you are hooked.
This is what happens: They will charge you hundreds/thousands in upfront fees, and ride off into the sunset with your money…
It doesn't matter what they call the fee - upfront fees are BOGUS. Reputable brokers charge their fees out of the proceeds of the sale/rental, after the sale/rental.