I suggest he visit the Timeshare User Group forum which is dedicated to timeshare ownership issues. He should be able to find helpful advice regarding renting from owners on Redweek and other rental sources. He should try to avoid renting weeks that had been exchanged using Interval International because rentals of exchanged weeks are not officially permitted.
Many people have had successful rental experiences (as renter and rentees on Redweek , so most are legitimate. Timeshares are different than hotels, so it is important to understand the type of unit and view that is being rented. If it is a week that the owner has actually reserved, the renter will receive the view and owner preferences of the owner. Typically, after the payment is made the reservations will be transferred to the renters name, and this can be confirmed with the resort..
I own 3 Marriott weeks and have used Redweek.com for years to rent out my unused weeks and have never had any issues. It's a two way street. Get as much outside contact info on the person you are dealing with. I never had a problem having people contact me directly at my workplace to confirm who I am. I wouldn't waste money on going thru a title co. Just do your homework.