I just want you all to know that if you pay me an agreed-upon ransom, I will honor it. The "agreed-upon" part is important; just transferring some ISK to my account and calling it a ransom looks more like a donation to me. But if I ask for, say, 20M ISK within 30 seconds, and you transfer 20M to me within that time, I'll turn off my warp disruptor and you're on your way--until the next day, of course. If you pay the ransom and I don't see it and I kill you anyway, I'll return the ISK (I've done this once already). But if you pay the ransom, I leave, and 5 minutes later some other pirate comes in and kills you, you don't get a refund from me even if my name shows on the killmail (killmails include the names of anyone who has "attacked" you recently, not just those who press the attack that actually turns out being fatal).
We talk about ransom a lot in the underworld. What should we ask for? When shouldn't we bother? It's all more of an art than a science. First, there's your ship. We can try to guess how much it's worth to you, but all we can do is guess. Sure, we may know how much the hull costs--but we don't usually know whether it has T2 fittings, best named modules, or junk; we don't know if it's insured or not; we don't know if it's rigged; and we don't know what's in the cargo hold. So we kill you without even asking for ransom when you're in a T1 frigate with a hold full of skill books and blue prints, or we may ask for 100M ISK thinking your empty hold is full of such treasure.
Next, we consider your clone. Are you wearing implants? We have no idea. Some assume new players don't have implants, while more experienced pilots are wearing at least a set of +3's. Once I asked for (and received) a small ransom from a moderately experienced pilot, only to find out later he had some pricey implants and I could have asked for much more; another time I killed a new pilot with very expensive implants, and he pointed this out to me after the fact. Most of the time, though, when I ask for ransom I'm told to forget it.
If you do have a valuable ship, cargo, or set of implants, and your pirate doesn't ask for a ransom, feel free to offer one. There are pirates that don't honor ransoms, but they are in the minority. Just know that by offering a ransom, you may as well say, "Hey, I have an extraordinarily valuable ship, cargo, or set of implants." The pirate may demand a higher ransom than he might otherwise be inclined; only you can decide if it's worth it or not.
Some pirates make a fine living off of ransoms; I'm not really there yet, as most of my targets are too inexperienced to have much wealth to protect. I'm told that in small gangs, whenever the leader tries to ransom a target someone else in the gang often doesn't get it and continues firing on the hapless victim until his ship (or his capsule) vents its gases and expires. And then there are the organized pirate gangs that offer a menu of services in exchange for various prices: they'll leave you alone for a day, a week, a month, even forever--if you pay the appropriate price. I'm not so sure this sort of ransom is worth it--there's always another pirate (or a dozen) waiting to disrupt your affairs when they leave.
Finally, there are those creative pirates who ask not for ISK but some sort of humiliating act--a post on some forum, for example (this can get the poster banned from the forum), extolling the pirate's prowess, or the recitation of a poem on the local communications frequencies. Some have asked difficult trivia questions, with the target's life dependent upon a correct answer. And some even pay an inexperienced victim more than his ship is worth, after taking some time to discuss the encounter and encourage the victim to make further forays into lowsec space. You should be so lucky!