Well... this is not that frequently... generally the problems on the first installation of avast that you've experienced are very rare.
I've seen issues quite a few times now that have required a reinstall of a trial version and the resulting lowering of the expiry period! There will be many occasions when trial users will simply try another AV product if they have problems days after installation. Why bother trying to fault find a product that is causing them issues when there are loads of other competing products they can try instead?
The 60 to 6 day antipiracy measure isn't one! There are cracks, hacks and serials available to those who look hard enough on the net.
This is nearly as bad a scheme as Windows Genuine Advantage :-(.
Here's a better scheme for antipiracy...
Make the default installation a 7 day and have a registration mechanism that allows this to be extended to a 60 day trial e.g. a webpage. Alternatively, make the registration a required step to activate the trial period from the moment it is installed. Alwil marketing can even use this as a mechanism to engage with the potential end customers.