I've noticed for the past little while that the used market in R0 is consistently empty.
More alarmingly, when the market resets each day, I open the page to find a selection of used aircraft for sale -- and then when I refresh (or try to buy something), the entire stock is gone. Instantly.
This will happen within the first minute of each in-game day.
Unfortunately it seems that someone might be using a bot to automatically purchase the entire used stock at the beginning of each day. Very unfriendly.