I'm almost certain there are. Speaking generally--not addressing southern New Hampshire specifically--many/most rent-to-own houses are legit.
Properly set up, it's a great win-win for tenant-buyers and sellers. It's not right in all cases, but it certainly is in some.
From your standpoint, you'd need to make sure that proper protections are in place. And that'd probably mean using a lawyer to review your documents. For example, you'd want to make sure that the owner couldn't sell the property to someone else while you had an option or contract on the property. You'd also want to make sure that the owner continued to pay his/her mortgage on the property. You'd also want to make sure that the agreement was for long enough to suit your needs. And if the house doesn't appraise for the needed number, that there's some provision in your agreement to address that.
All of those items are very important to protect your interests. On the other hand, they're all relatively simple to accomplish.
Again, though, most rent-to-own arrangements are legit.
Hope that helps.