In any development arrangement between a customer and a software developer for bespoke software, it’s vital that you deal properly with software testing and acceptance.
In the absence of a paid-for support service, most developers offer only a limited warranty period after acceptance so customers should ensure that they are not deemed to have accepted any software release until they have had the opportunity to test it and sign it off. Customers should resist any provision that assumes acceptance just because they’ve allowed a given number of days to go past without reporting any issues.
On the other hand, if you’re a developer, you should ensure your customers cannot unreasonably delay acceptance. If you’ve agreed that acceptance doesn’t happen until they’ve tested and signed off the release, then you should agree a backstop date to ensure they don’t prevaricate.