If I'm playing against a large field preflop then I might worry about a draw. In this situation I wouldn't. I would call his bet and let him bluff at it again on the turn - and call that (or raise to pot size if I think he'll call it.) On the river, obviously raise/bet as much as you think he'll call.

You have to gamble a little. Flopping trips is as close to a sure thing as you'll get with action. Typically you'll see more people drawing to the flush than the straight. If he has A4 or A5, he's still drawing to a inside straight. I'm hoping he does have it and that an A comes on the turn or river. That's where the money comes.

If he has nothing, then you'll get paid very little. You string this out as much as practical to let him hit something and figure he has you beat.

You can't worry about everything all the time. What if you flopped 2nd high trips, how much are you going to worry about someone having a higher set? Extract as much money as possible and give them as much opportunity to hit something like a high pair.

If you're playing 7 handed preflop into an unraise pot and 2 of the same suit fall, then you need to bet harder - although, at these levels people may call anything on a 4 flush. So there's never such thing as a sure thing. But getting trips with a pocket pair is a monster hand and you should get as many chips as possible with it. The bad thing about this flop is that no one could have flopped a big pair, so it's hard to get action. So, give him a card and let him get something.