Sounds funny but you actually can. Trying a house out would could be possible by renting it for a while before buying it. That way you would know if you really liked the house, if the property is what you thought it would offer.
But if the current owner wants to sell the property he does not want to rent it as this might hinder a successful sale. In a slow market when the owner is not occupying the property (investment property) he might be willing to rent the property with an option for the leaseholder to later buy the property.

There are various permutation of how such a deal can be structured. The future purchase price could be predetermined which would be similar to an option in the financial market that can have intrinsic value. Or the future purchase price could be the future market value which would be negotiable between buyer and seller or could be determined by one or more appraisals.

You can see the variations are endless and a creative mind will go a long way in finding a mutually beneficial proposal.