Seasoned pirates that shoot at you only do it because you're trying to run away and not give in to their demands.
If you think you can run and successfully escape, by all means give it a go (I know some of my mining ships will, while others won't, so my response will depend on which ship I'm in). That's a calculated risk you're taking as you normally get a warning from said pirate ("don't run or you will be attacked").
I'm not a seasoned pirate and have done this maybe 5-6 times in various scenarios - once I joined a pirate wing who were quite organised (their ships and builds complemented each other well for the task), I was in my pirate Cobra 3 at the time. Before they invited me they asked whether I PK or not, I declined so got the nod to join.
We interdicted a T9 in a high-buying LTD system. The T9 got several warnings to stop and provide LTDs (can't remember how much but it wouldn't have been the whole load) - presumably it was full so 700+ tons.
For some weird reason the T9 tried to run, we attacked as a result, slowly chipping away at his hull, then pausing, then trying to communicate, rather than just whacking them (we were after the cargo, not the ship).
They kept trying to get away (in a T9... it's not impossible but he didn't high-wake and it wasn't the most sturdy build either). He eventually popped, it was tragic as he could've avoided both losing all his cargo and eating a rebuy. We still got about 30t of LTDs so not completely unsucessful. Oh well.
Edit - I also want to say fair play to that T9 CMDR for a) playing in Open and b) not logging on us. Thing is, he would've most likely gotten a free escort to the destination if he'd yielded, and maybe a few more players on his friend list (even gankers don't tend to grief you if you're friended - most players are rather nice and reasonable, exceptions notwithstanding).
Look, I know its a game, and for many people that excuses just about anything. My initial reply was more about his choice of words: the idea that his "client's" hull wasn't strong enough to take the missile hits... What you're describing is one of the least evil variants of ED piracy I've seen, but if we're talking about role-play and career path - there's no such thing in ED. Piracy carries nothing like appropriate consequences for the pirate. As has been pointed out countless times, all the risk falls on the trader. The lack of response from the existing political institutions is relatively ahistorical Pirates were and are hunted. What we're left with is something on the spectrum between griefing or ganking. Piracy needs a viable career-path, some actual threat to the pirate, and the obvious material reward to the trader who was willing to brave pirate-infested space-lance to get those LTDs to market.