Don’t bog yourself down with this nonsense.
for example, I have had a bumper May and June yet my fellow traders are having a mare.
My average time in stock is 20 days, what bollocks this is. I sold a Passat in 6 hours and have a BMW for 86 days - the average means Jack.
you just have to trial and error - for example, I will never buy a Fiat 500 again (time in stock), never another Land Rover (cost to prep and warranty), never an odd ball colour, etc etc.
Averages are a pointless exercise, look for problem cars and avoid them.
Above all, go and buy some bloody stock instead of looking at stats which are skewed by large franchise dealers whom offer supported finance, extended warranties, service plans etc (all stuff you can’t). Whilst you’re wasting time looking at stats you’re earning diddly. Buy something you might make a few quid or lose a few quid but at least you’ll be doing something meaningful and learn something tangible.