ask to ride it and then offer 175.

it won't 'automatically brake' when you stop peddling because you won't stop peddling until the bike stops. you can push either way on the pedals and by resisting their rotation you can slow to a stop, but you will want to use that front brake to actually stop, especially when you first get on it.

i say go for it... even if that's a lot more than i bought my 80's fixed conversion for... i got lucky