… there are three methods of Customer Validation that increase in the cost of execution. None of them involve writing code, which is even more expensive to execute.
1. Exploration Method
The goal of exploration is to collect a lot of data on potential problem sets within a given industry or customer type, and to collect detailed stories on customer behavior.
2. Pitch Method
The Pitch method is about getting customers to give you a form of currency .
3. Concierge Method
Concierge is delivering your product through a physical service, hand-holding the customer. This method has also been referred to as Wizard of Oz, ie. faking the product with as little technology as possible.
(via How to Get Out of the Building with the Validation Board )
See also Tips on choosing your customer learning method for help on how to choose which method is appropriate.