Always check out used bikes thoroughly or even take it to a bike shop to get checked out. If the seller expresses concerns about either, that's a huge red flag that something is wrong.
micromobility - Bikes, scooters, boards: Whatever floats your goat, this is micromobility
Ebikes, bicycles, scooters, skateboards, longboards, eboards, motorcycles, skates, unicycles, heelies, or an office chair: Whatever floats your goat, this is all things micromobility!
"Transportation using lightweight vehicles such as bicycles or scooters, especially electric ones that may be borrowed as part of a self-service rental program in which people rent vehicles for short-term use within a town or city.
micromobility is seen as a potential solution to moving people more efficiently around cities"
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It's a little sad that we need to actually say this, but:
Don't be an asshole or you will be permanently banned.
Respectful debate is totally OK, criticizing a product is fine, but being verbally abusive will not be tolerated.
Focus on discussing the idea, not attacking the person.
If someone is describing jockey wheels as "middle derailleur hubs" and that replacing this one part will somehow cost almost as much as the bike, they don't know enough to be buying a used, complex machine. Ya know, the machine that one is putting between their legs and riding down the road.
Unethical seller? Most likely, and the blame probably rests on the seller, although I'll give some benefit of the doubt here. If someone bought one of my bikes and had such an issue, I would be aghast. I would bend over backwards to make it right.
There are so many subtle ways that a used bike can be a bad deal at any price. Please let this person's experience be an opportunity to learn. Read a couple articles on what to examine when buying a used bike, how to determine if a frame is true, and how not to get screwed by a shady or just plain ignorant seller.
And FFS, take a few minutes to understand the rudiments of the systems on which you rely AND spend your hard-earned money.
Shout out to ParkTools YouTube channel for bike info and maintenance.