Is it just me, or are there a lot more HITs that have a minuscule initial payment (say a couple of cents) and then a large bonus at the end? I think this practice is a bit shady. Doesn't this allow requestors to entice workers for longer more involved work with no guarantee to be paid? As far as I know, bonuses don't have to be paid and are completely up to the requestor's discretion. They can approve for a couple of cents, get a ton of research, and then chose not to pay the bonus for any reason, without recourse. As far as, I know bonuses can't be disputed. They keep their approval ratings high. Also, I don't always keep track of bonuses I was "supposed" to get, so I have no idea of how much I have left on the table. I thought bonuses were supposed to be reserved for exceptional and thoughtful work, and not as the main compensation.
If you note the bonus in your review, TV will track it for you. This also helps with your other problem, letting people know that the requester is a deadbeat.