It's pretty obvious when a Ret healer knows what they're doing.
Just pull a pack and keep track of your health pool, if you're constantly at the brink of death kick the Paladin because he clearly doesn't know what he's doing.
A good Ret healer can heal through most heroic trash with just default Battle Insight. I only ever need to use FoL to top people off in between pulls or during periods of heavy damage.
You as the tank can make that decision for yourself. I've never had a tank even question my being Ret once the dungeon's started because he never has a reason to. They don't need to change their pulling patterns out of fear of dying and my added damage just allows us to clear the dungeon a whole lot faster.
True. I'm not saying I would insta-kick the Ret healer. I'm just saying that as a courtesy sort of thing I would feel better if the Ret healer gave a quick hey-no-worries hello, rather than making me go hope this is one of those that knows what they're doing as I do a couple little nervous test pulls. Since many Ret healers seem to be doing okay, and yet there are a significant number of tanks who get upset at the sight of them and want to kick anyway, I just think saying a little friendly something could relax them (tanks) a bit. Once the tank has a couple good experiences they will probably be more chill.