By all means, advise, discuss or even criticise on actually playing with the cars but leave other's business alone.
It's usually the same people piping up time and time again. They buy a car on here and "quietly" sell it elsewhere making a few grand profit and stripping off the nice parts. That's perfectly fine but how would they feel if their selling strategies were commented on? Do we all tell them how to sell and at what price? No....
The guy is selling his car. Is he an adult, can he make his own decisions? Probably that's a yes. If he gets his pricing right or wrong so what? Let him find out through his experience. Maybe the speed of sale isn't so important to him
If you're not interested in buying stop casting doubt in potential buyers minds with continual comments. It's not fair to the seller... Leave him to find his way. Would those that question pricing like the same when they sell?
Of course there is the mutual backpatting brigade to consider... The one's whose mates say what they're selling is well priced, a bargain, glws etc
Anyway, just respect that it's not your car to "sell" on their behalf at a suggested discount of your choice....