To chime in on the discussion of professional brokers and market makers. Not being an economist, not having read any papers on the matter, this is purely circumstantial and anecdotal evidence. But I have a feeling every marketplace is eventually taken over by the pros, from eBay to its copycats (e.g. Carousell here). Initially it's a chaotic heaven with deals to be found and pigeons to be feathered. Then slowly the deals are harder to find and people wise up to the price history before purchasing, and eventually new stuff appears as shop realise it's a cheap/free marketing channel and piggyback on the brand mindshare, and before you know it the regular users are mostly gone. I remember using eBay a lot more 10 years ago than today, although if I use it today it is to arbitrage international price differences or get a specific SKU (e.g. the US Garmin Fenix has software updates 6 months ahead of the APAC version, so worth waiting a few weeks shipping) from a professional shop. Similarly AirBNB is now almost entirely pro, Uber driver is an actual job with rental companies providing a specific contract just for it, etc.
All this to say... yes, price discovery becomes more efficient and some kind of liquidity is provided (and paid for, compensating the efforts of said market makers). But there's knock on effects that inflict less visible damage. I miss the days of discovering really cool neighbourhoods and people with AirBNB (and Couchsurfing), or the retired guy in his Rolls who picked us up on standard Uber in Point Piper, Sydney because he liked to "meet interesting people".
All this to say... yes, price discovery becomes more efficient and some kind of liquidity is provided (and paid for, compensating the efforts of said market makers). But there's knock on effects that inflict less visible damage. I miss the days of discovering really cool neighbourhoods and people with AirBNB (and Couchsurfing), or the retired guy in his Rolls who picked us up on standard Uber in Point Piper, Sydney because he liked to "meet interesting people".
