Word for saying product is good after buying it even if it's really not
Google turns up this wikipedia article which currently reads:
Post-purchase rationalization, also known as Buyer's Stockholm Syndrome, is a cognitive bias whereby someone who has purchased an expensive product or service overlooks any faults or defects in order to justify their purchase. It is a special case of choice-supportive bias.
This is the answer to your question, is it not?
Sounds like an attempt to save face.
To take an action or make a gesture intended to preserve one's reputation or honour.
Wiktionary.org