I guess, in the eyes of some, all dealers are, at their core, unethical. They take trade-ins, do little or nothing to a vehicle and then sell if for more than what they paid for it.
I don't see dealers doing that as unethical in the least. Why would some apply a different standard to private parties who flip bikes?
If someone has a bike listed for or sells a bike for less than what the supposed market value is then that's their decision. If a flipper didn't buy it at that price then someone who intended to own/ride it would. Doesn't that make that person equally unethical in that they somehow "stole" from the buyer by paying less than market value? In my world it doesn't.
If I bought a bike for a grand, did nothing to it, and sold it for two grand the next day with no deception involved then I'd consider it completely ethical regardless of what some pansy stranger on The Interwebz thinks.