At charm 150 and trade 225, it's quite easy to get someone to join. There is still some save scumming you'll need to do, but otherwise doable. Some folks will *not* ask you for a bribe after doing a trade. If they *do*, you might have to sweeten the pot with up to 800k or gifting them fiefs. Note not to pay attention to the bar icon, just wait and see when the 'offer' button is no longer grayed out.