When I'm pirating I always tend to RP, i usually say something about the ship or the cargo, and sometimes i negociate with them about the tax, and how much does he make on that route, I don't know all the prices for all the commodities, but i know enough. I hate it when the first thing they'll do it's tart their cruise engines, thenI tend to be a mean pirate, and the further you take me from my place, the more the fine raises. Most of the time i tend to tax from 500k to 1 mil depends on the cargo, but if you make chase ou and afterwards thinking of paying, i also apply to the 30 seconds rule. You just have to be nice and cooperate.
On the other hand, when I'm trading I sometimes, stay and RP, sometimes try to escape(once i fled from 4 pirates in california 1 GB and 3 VHF, and they followed me until we were destroyed for being outside of the system or something like that:D), sometimes i exit the lane before i reach pirates and TRY to escape but mostly i wait for them to "make their offer", if it's over 2 mil don't think so, if it's worth more than the cargo, I don't think so, if you catch right after i bought the cargo and you ask a price double or triple, I really don't think so.
Seems like everyone has it's own way of handling the situations.