I am not a lawyer either, but here's how I see it:
A sales agreement is a contract between you (the first party) and the buyer (the second party). The clause you have quoted says absolutely nothing about anything that happens between the first party and the second party.
What the clause does say is, the program itself must be available free of charge to all third parties, i.e. anyone who has not entered into a sales agreement with you. So, if the program is the only thing you're actually selling, there is no incentive whatsoever for me to enter into a sales agreement with you and pay money for it when you're required to give it to me for free. If I'm the kind of person who wants to pay for it, great, but you'll probably go out of business if you rely on finding that kind of person.
So, in order to induce me, a third party, to become a second party and enter into a sales agreement with you, clearly you should be offering some added value; warranty, support, installation services, hosting, etc.
