I only ever pirate on house pirate IDs. I haven't had a trader complaint in an extremely long time, and I am a quintessential pirate king when it comes to organising mass piracy situations.
The general rule is; roleplay well, treat traders as a potential PVP asset when they run, and give them a fight proportionate to the travel distance they'll have to cross. If they're very close to a base, fire every available weapon system. If they're a bit further away, give them more of a chance.
Always be a satisfactory encounter.
Treat traders who are prepared to RP respectfully. Sometimes the best piracy encounters aren't for credits, but to fulfil an InRp objective. - for example requesting that a neutral-IFF'd trader ships commodities to a sellpoint with the same IFF, instead.
THE SYNDIC LEAGUES
(A co-operative of Rheinland's Shipping Unions, retired from a life of piracy.)