Yes, advertisers can and do try to invade subreddits posing as "real" users to promote sham products. But I haven't seen this actually working: sometimes Redditors recommend products which are way too expensive (still good quality, but the extra price really isn't worth it), but if someone recommends a genuinely crappy product, they get downvoted and replies saying "don't buy this"
Advertisers and shady affiliate marketing schemes have caught on and nearly every search result I try is now filled with junk, upvote farmed nonsense with fake accounts using similar naming schemes.
The top post in the relevant enthusiast sub recommending stuff to buy had no actual information, but it was stuffed with Amazon affiliate links. It was basically a "Top 5 X 2022" post except it was on Reddit instead of its own spam blog
So many of the Reddit threads were blatantly astroturfed.
By the way, while I have you here, have you considered extending your used car's warranty?
Would you know if it did?