max gate distance to buy/sell?

[DrwHem]

is this determined by the station manager or the pilot of the trading ship?

[Wraith]

If you have a station it by your station manager as he leading the trade ship and they will use his skill instead of their own.

[Gregorovitch]

I believe it's coded such that individual station traders/miners use either their own pilot's piloting skill or the station manager's management skill, whichever is the greater.

But since station managers level up fast and trader/miner pilots hardly at all, for all practical purposes travel range is determined by the station manager, one gate per full management star.