But won't everyone say yes to something free?
These people are usually busy people running their businesses. There was a Mixergy interview with LessAccounting where they said that people searching for "Quickbooks replacement" on Adwords were not sufficiently motivated to replace Quickbooks. The revenue earned from Adwords covered a third of the costs.
In Steve Blank's "4 steps to Epiphany", the enterprise customer who was a apparently close to buying (according to Sales VP). Eventually, when this question was asked... "if it was free, will you deploy it straight away?" the answer came back as "no, because it was not urgent, etc".
To expand a little bit further, sometimes people see value in expensive stuff just because it has a high price tag.