Why you need one: No matter how good a house looks and no matter how much you love it, you want to be sure it's sound structurally and in every other way. If it's not, you want to know whether the seller will address the issue before you seal the deal. If not you have to decide whether you want to back out of the deal or take care of the repairs yourself.
When it needs to be done: Many states require that inspections be done within five days of the seller accepting your written offer; others may allow up to 10 days. Whenever it is, "go to the inspection. There's nothing more important you can do than that," said Frank Lesh, president of the American Society of Home Inspectors (ASHI). You'll learn a lot more about the home than you would otherwise and the inspector can give you good maintenance tips.
When to call: Given the relatively short time-frame you have to conduct an inspection, it's smart to call an inspector before the contract is signed (but when it seems likely that it will be) to make sure you lock in an appointment when you need it.
When the inspector recommends fixing something: Say the inspector finds something wrong such as mold or water damage. Talk to your real estate attorney to determine your next step: it might be to ask for a price reduction or to ask the seller to arrange and pay for repairs. If you choose the latter and the seller agrees, be sure to get a written receipt of all the work that was done. That will give you recourse in case less work was done than the seller agreed to do or the work done was shoddy (e.g., unsafe electrical wiring).
Cost: $350 to $1,000. "Generally speaking, the larger and older the home, the more you'll pay," said Frank Lesh, president of the American Society of Home Inspectors. Likewise, if you live in a high-cost area you'll pay on the higher end of the range.
Where to find an inspector: ASHI-certified home inspectors in your area can be found here. You also might ask neighbors and friends if they have used an inspector before whom they liked. Make sure the inspector you choose has experience working in your area and specializes in the type of residence you're buying (e.g., single-family home vs. multi-family building).