> But if an account runs for a longer period of time and makes a lot more general organic contributions then if 1 in 500 of their comments are in favour of a particular product then it's harder to say.

I've made recommendations a lot more often than that back when I used reddit just through being active in a specific niche-ish subreddit and regularly answering questions with answers that end up saying 'buy [well-known good product that solves this exact problem you want solved]'. Then again, my account was several years old by that point, and I was recommending probably 4-5~ different products depending on the question, all from different sellers, not to mention that I'd answer all kinds of different questions, building goodwill and recognition, so accusing me of being a bot (or just a human who has a financial interest in promoting certain products) probably wouldn't do much, but if you want assume ill-will, it'd be really hard to truly disprove that kind of accusation.