I think the author means "vaccinated". They mean that they've been made resistant to buyer's remorse.
It should be "inoculated against" but the meaning is clear.
A vaccine inoculates you against a disease by a physical mechanism: that is, it prevents you from getting that disease (to a greater or lesser degree).
Metaphorically being inoculated against something means it can no longer hurt you. For instance, maybe by not owning a car you're inoculated against vehicle depreciation. Or by wearing the same simple but quality outfit every day you're inoculated against the vagaries of fashion.
Non native here. What's the meaning of inoculate here?
It's not the first time that I struggle to parse this word. In italian it keeps the original latin meaning and can be translated with "injected with". You could inoculate a vaccine but you could also inoculate a poison, so it does not carry the immunity meaning by default. English (US?) as far as I can tell use it as a synonym of "immune", is that so?