It's hard for me to get all bothered about this. I've rented/exchanged my timeshares to other people in the past and I've rented/exchanged from owners in the past. I've never given VSE's number for prospective renters to call, nor have I ever demanded a reservation line to call. Admittedly, I don't rent from Craig's List or eBay, which seem rife with fraudsters. Rather, I use Tug or Redweek, both of which require a modest membership fee to join. Thankfully, most fraudsters can't be arsed to fork out $10 in order to defraud people.
When I rented my VOIs, once we reached an agreement on price, I provided my full name, home telephone number, home address, and a screen shot of the "My Information" page and proof that the MFs were up to date. I also invited them to google my county's property tax information records to verify that I'm who I say I am. (Hint: property records are often searchable and free if you know the county (which can be looked up based on their address), as it's public information.) Once I received payment, I sent a screen shot of the reservation with their name on it, and forwarded the email confirmation of the reservation. I also went online and checked the box for Vistana to send the guest a confirmation, which lists the villa type, date, and view (if applicable). That's it. When I rented from another owner, I asked for the same info.
So if I was in the business of renting timeshares, I'd change the prospective renters' expectations and simply quit offering the ability to call reservations directly. If they insisted, I'd schedule the three way call. Otherwise, I'd offer the ability to secure their reservation with PayPal, which accepts credit card payments (and consumer protection). If what I've offered doesn't satisfy them, then they're going to have to miss out on a good deal. No risk, no reward.