@OmSigDAVID,
It depends on the past lie(s), the motivation of the liar, and the possible veracity of the person's future statements.
If the person lied to protect the feelings or whatever of the person he was lying to then a little more weight can be given to his future statements of alleged fact. Then again, if the person's lies were unnecessary protections ... say a little too much on the patriarchal/patronizing side then perhaps his attempts to persuade in the future maybe taken with a mere grain of salt.