that guy could even be the owner, the son of the owner, a relative of the owner or just a random guy who's been told that they MUST sell more 21' (left in their stock) than 27'
after all he is there to sell
if everybody goes there and asks the 27'', he/they must convince people to go for the 21''
and they succeed once they did.
if you have funds+space go for the 27'' and thank the guy for his advice.