Very rare for a Bally Star Trek to have a ''great condition'' playfield, I have not seen one original that was not worn in some way.
However, CPR has done a run of playfields, I bought one from them as I have two Star Treks. One of mine is a great player, the other is in pieces but just about all there)

Other area of concern with these is the backglass, especially at the bottom (they bubble or flake) I got lucky with my two, one is very nice and one is near perfect.
Check for battery acid damage on the cpu, very common. Fixable, but a pain in the ass. Alltek cpu is a better bet, or a good solid used one for half the $$

I'm guessing the capacitor could be anything from the sound board or the driver board. The sound boards are rare/hard to find but if it's present there are people here that work on them. More than likely he is talking about a driver board capacitor. Alltek makes all the boards (except sound board) for these pins.

If things check out okay, then the price seems reasonable to me.

Good luck, fun pin.

The backglass you should be able to ''seal'', they are very hard to get as a replacement, so if it is something you can live with, (not having a perfect backglass) sounds like that backglass is okay.

At $400-450 you can't go wrong if you're into this style of game/early SS bally. It's a really fun game, fun with friends too.
The playfield, you can either play the hell out of it, try your hand at touchup or grab one of the few remaining CPR playfields hanging around and do a playfield swap.

I say go for it, what can you lose? Hell, the sounds board if it works is worth a $100 bucks all day long.