Make your offer contingent on an inspection. Then, if/when your offer is accepted, you have it inspected.
There are times when you might want it inspected before making an offer. For example, if there's a possibility of major structural damage and you need to know whether you're looking at a $10,000 repair or a $70,000 repair, then it'd be difficult to make an intelligent offer without knowing more.
I'm not sure who you would sue. You could try to get the agent's license revoked if he/she did something wrong. But to sue, you'd have to show monetary damages.
Further, suing wouldn't have much of an effect on you getting a mortgage. Being sued is a different matter--then there's an unknown liability hanging over your head. But suing someone else? That shouldn't be a problem.
As far as pursuing (in any way) a house you cannot purchase: Don't do it. If you can't buy it (because it's not for sale, because it's way over your price range, whatever), then walk away.