Marketing includes sales as well, and REIN teaches some excellent strategies.
I had written a very detailed reply, but a website error deleted it, so here is the executive summary:
1) "Instant Rental Approval" can be offered to quality prospects. This holds the suite for them while their references are being checked. With only a $100 deposit against the first month's rent, they have the peace of mind of knowing that no one else can take the suite. Forms are available on REINspace (possibly to members only).
2) If the prospect doesn't want to take advantage of that offer, ask why. Perhaps there is something unappealing about the property that you hadn't noticed.
3) REIN has an excellent module about preparing a property for rent and what renters consider most important. For instance, curb appeal is often more important than amenities.