I have a great amount of disgust for the attitudes these agents have in reguard to getting a property under contract and the further negotiating of the terms after they have gotten the property off the market. Contingencies at one time were used just to protect buyers from conditions that were not easily seen at contract signing. They are now often being used as a tool to put the buyer at an unfair advantage after the seller has lost the value of a fresh listing. If a buyer backs out because he hasnt done his homework or can't get the price down further, the seller has to return to the market with a less fresh listing and a stigma of falling out of contract.
May answer as to what you need to know before you make an offer is basically "everything" with the exception of less than obvious defects to the structure or situations that need environmental testing. I know that is probably not the answer you were looking for but I am a guy that turns over every stone before I act.