If you make a low-ball offer you won't even get a counter offer in a hot market.

In a slow market you want to price to sell. If you price too high... you'll knock yourself out of the running.

Unless the contract says 'as is' everything is up for negation. Even then, the buyer usually still has the right to ask for repairs or back out of the contract.

The seller can try to negotiate with his or her agent for a lower commission if you don't have an agent. But they aren't obligated.