I don't know which listings you're looking at, so I can't comment specifically on them. But I can comment on the concept of rent-to-own and lease-options.
I'd answered a similar question a little while back, so I've modified that answer for you. Here's the link to my original post: http://www.trulia.com/voices/Home_Buying/Do_lease_rent_to_ow
Lease-options/rent-to-owns are not scams. They are not shady. They exist. They work. In many situations, they're win-win situations for both the tenant-buyer and the homeowner/seller. I wouldn't say there are "catches," but there are situations in which they're appropriate and situations in which they're not. So the "catch" pretty much is: Make sure it's the right solution for you.
A little bit about lease-options: They work well when someone (a tenant-buyer) wants to purchase but is unable to. Often the problem is weak credit. Sometimes it's lack of a down payment. A lease-option allows the tenant-buyer to find a home, control it, and lease it for a predetermined time (often 2-4 years). The option portion gives the TB the right (but not the obligation) to purchase the home. Depending on how the option is written, the TB may have the right to purchase at any point during the option period, or maybe only at the end. Usually, the option specifies an exact purchase price, but sometimes it may specify an exact way of determining the purchase price when the option is exercised. Often--though it's always negotiable--the TB pays an upfront option fee that's credited toward the purchase price IF the TB exercises the option to purchase. And often a portion of the rent you pay is also credited to the purchase price.
The couple-year time period gives the TB the ability to clean up his/her credit. It also helps the TB reduce the purchase obligation, since a portion of each month's rent is being credited to the purchase. And if the TB doesn't like the home, then at the end of the lease he/she can just walk away.
Most agents don't understand lease-options, as you can see from the comments on my earlier posting. I'll restate a few here (what some would consider "catches") and give you the answer.
To give just a few examples: "In this kind of market lease options are far and few between."
That's bull, to put it politely. In this kind of market, there are more lease-options than you could possibly imagine. And that applies nearly everywhere in the country.
I wrote a blog on how to find lease-options, which gives a lot of ways to locate them: http://www.trulia.com/blog/don_tepper/2010/03/how_you_can_fi
Believe me, they're out there.
Another comment from the earlier thread: "You would have to put up Option Money, let's say approx. $10-15K and if you don't option the purchase you could lose that money." The amount of the option fee is negotiable. Often it's around 2%-4% of the purchase price of the property. But I've lease-optioned property without paying a penny. (For those of you wondering what the "consideration" was, the consideration was the $17,000 lease I signed.) And yes, usually you forfeit the option fee if you don't exercise the option. So, some people would consider that a "catch." But the point is that you've received something of real value for your option fee: The right to purchase a property at some point in the future for a set price.
Another comment from the earlier thread: "If the property value goes down over the next year, you'll have to renegotiate you purchase price and it may be with the bank." I'm not sure what that means. If the property value goes down, you're in the driver's seat. You can let the lease expire and just walk away. You're not forced to buy the property. Now, if you want to buy the property, you renegotiate with the owner. The bank has nothing to do with it, unless the property's been foreclosed upon. In that case, your option is worthless and you have no more right to purchase anyway. But there are ways to protect yourself if there's a concern about foreclosure.
Bottom line: Lease options aren't for everyone. But they're great for people who need them, and they're great for owners with vacant properties or properties they've been unable to sell. (In today's market, that covers quite a few owners.)
So, yes, they're legitimate. If you're interested in pursing it further, make sure the Realtor you use knows, understands, and is comfortable with lease-options.
Hope that helps.