Learn English – the opposite of heritage

An idiom for this situation is the pot calling the kettle 'black'.

A fitting term for a person who does this is hypocrite; though the exact meaning of that word is someone who pretends to be what he is not, it applies because the person is pretending to be better than whom he is denouncing, while in reality he is the same.

If you want to look at it from a psychological standpoint, using that terminology (suggested by Henry), you could consider psychological projection (aka projection bias):

Psychological projection or projection bias is a psychological defense mechanism where a person subconsciously denies his or her own attributes, thoughts, and emotions, which are then ascribed to the outside world, usually to other people.

Psychological projection appears to be the most common and unambiguous term; referencing google searches, I find that projection bias may sometimes be used to mean something else.

I have in fact encountered the word downsell, in colloquial and semi-formal contexts: insurance salesmen and financial advisors use it in discussing the need to dissuade clients from purchasing financial products with attractive "features" but dubious benefits.

He was convinced that the universal policy would guarantee his retirement, and it took a lot of downselling to show him he could accomplish the same thing with a convertible term policy that fit his current budget without the risk.

Upselling is deprecated by sophisticated salespeople in the insurance industry, because it's typically a one-off sale, with a greater risk of lapse. Downselling leads to longer-sustained relationships, which are ultimately more remunerative for both the agent and, they believe (or at least maintain), the client.