I think it will be difficult to remove bias when you ask a model to compare alternative products. The model will simply lie, as with a biased human opinion and you will need to consult multiple models for a diversity of opinion and presumably use a "trusted" model to fuse the results. Anonymity will be a key tool in reducing the model's ability to engage in algorithmic pricing.
Writers have many options to deceive their audience without outright lying.
If a journalist is given an all-expenses-paid trip to an exotic location for the launch of a new product, and they review the product and say it's great - are they lying?
If a reviewer writes an article comparing certain types of product, but their review only includes products where affiliate links pay a 10% commission - are they lying?
If a journalist is vaguely aware of rumours about newsworthy, under-reported Event X but also that their publication has a big sponsorship deal with folks that Event X makes look bad, and they don't investigate the rumours or report on them - are they lying?
If a reviewer hears a claim from X, and they report the claim credulously, without adding the context that X has a history making false claims - are they lying?
I'm using bias to mean hidden motivations to the benefit of other parties. Feel free to substitute a better word.
EDIT: actually I'm really not sure what hairs we're trying to split here. I see bias as a departure from objectivity. It can be conscious or unconscious, but when someone is selling something, it's frequently conscious and self-serving, and I believe that's referred to as a lie.
This would be where you post-process the LLM response with a second LLM to remove the ad..