@OP I am agreeing with you here. Getting rid of your bounty is way too easy. I'm in agreement that an NPC bounty should be what it is and wipeable -- but a player bounty should be set by the TRANSGRESSED player.
This, in my opinion does a few things; firstly, no little expert cobra is going to interdict a dangerous or elite t7 and demand his cargo, as soon as he does; wham, 100,000,000 cr bounty he couldn't wipe in MONTHS. This will give traders more power -- balance and will give pirates pause from trying higher ranked traders. This can also open up a whole new aspect of the game: bluffing -- a trader can simply tell the pirate, "Run away now and I won't put this 5,000,000 bounty on your head for the interdiction".
There are a few things I look at when I dream up mechanics like this: Can you exploit it to grief? No. Is it fair? Yes.
Can you exploit it to grief? No.
Absolutely not. If you don't want a bounty, don't kill someone in cold-blood and don't rob them. Simple as that. If the only way you can get a bounty placed on you is by an interdiction of a trader or by being killed (not assaulted) by a player, then a player should be able to put what ever bounty they want on a pirate. Pirates already have very little risk while pirating and can easily wipe what little bounty they have, unlike bounty hunting bares a great risk with little bounty and trading -- well you're flying a flying paper can full of gold; anything that attacks has nearly zero risk. The risk needs to be in the credits. Pirates need a risk, and a player paid bounty is one of them.
Now most players aren't going to dump 10,000,000 cr bounty on someone, but if said pirate keeps ing off elite traders, he can expect to quickly get a 10,000,000 cr bounty. At some point the pirate will have to weight whether or not his exploits are worth it. Some sense can be used in picking the right targets -- like expert traders flying a brand new, T7, which you know good and damn well they don't have a wad of cash on hand to place bounties.
Is it fair? Yes.
Absolutely. If you murder a player, that player should be able to place a bounty on your head that the only way you can get rid of it is to die and have your credit loss subtract from the bounty (payable to the bounty hunter). This balances the power between bounty hunter, pirate, and trader -- giving the trader power of the purse, pirates power of cunning, and bounty hunters power of brawn (I'm personally liking the sound of this).
If you're a pirate, you likely loathe this idea in open play being its taking away your easy mode. If you're a trader, you likely love this idea because it gives you some recourse and a bargaining chip, and if you're a bounty hunter, you're likely over-joyed that you can actually make the same money a pirate can.