It's in-rp to not pay the tax. Run from the pirate, shoot the pirate, but sitting there and saying "just kill me" is not good rp in the vast majority of cases, and adding the "it's cheaper" is blatant use of game mechanics, which your characters should be oblivious to. That said, while it should be frowned upon, it shouldn't come to sanctions.
Whether or not you pay depends on the nature of your character, and the pirate's demand. I usually pay, because my Zoner values his life and that of his crew. Plus he doesn't have the pressure of punishment from a corporate boss. Most pirates as of late have been fairly reasonable. Sometimes you get taxed more than the sell value (for example, someone recently asked a $1m tax on my shipment of water with a $600k sell price), but that happens sometimes. If you explain, the pirate will often lower his price.
The only truly whine-worthy event for me was back in 4.84 when two corsairs with bad english in lunchboxes asked for $6mil tax on a food shipment to Crete, two jumps away from Crete, whilst ramming me all the while.
As a pirate, I try to be fair. I know I'm not going to get rich on piracy, and in fact my Rogue can barely keep his ship pieced together (takes the occasional /givecash charname 1000000 to cover ammo and regens). I pirate for the fun rp of it, and usually don't ask much- a few hundred thousand, or 50-75 units of their cargo if I can sell it on Rochester or a Rogue base, or if my character just decides he likes the cargo. But each pirate is different- some bloodthirsty, some just desparate to survive; some greedy, some not. Since my pirate usually works alone, he is in a weaker position as well.
But as with anything in Disco, the key is roleplay- always have a reason (unless you play a crazy person etc.), and know your character, who they are, what they do and why they do it.
