PostgreSQL Data Loss

Hi everyone,
I have a problem with one of my costomers.
I made a program that uses a PostgreSQL (win32) database to save its data.
My customer claims that he lost lots of data reguarding his own clients
and that those data had surely been saved on the database.
My first guess is that he is the one who deleted the data but wants to
blame someone else, obviously I can't prove it.

Could it be possible for PostgreSQL to lose its data? Maybe with a file
corruption? Could it be possible to restore these data?

My program does not modify or delete data since its more like a log that
only adds information. It is obviously possible to delete these logs but
it requires to answer "yes" to 2 different warnings, so the data can't
be deleted accidentally.

I have other customers with even 10 times the amount of data of the one
who claimed the loss but no problems with them.
He obviously made no backups (and claims whe never told him to do them
so we are responsible even for this) though the program has a dedicated
Backup-section.

Any suggestion?

Daniele