This thread dates back quite a way, but since there's a new answer posted, I thought I'd add mine . . . particularly since I strongly disagree with the advice provided here.
But first: I'm not licensed in California and so my advice isn't directed specifically at California. Further, customs and expectations vary in different places. If a seller lives in some place where an agent says that pre-sale inspections by the seller are expected, then seriously consider doing it. Okay?
As the answers here note, the buyer is very likely to get his/her own inspection. And that's the right thing to do. That's going to happen whether or not you get a pre-sale inspection.
What are the advantages to a pre-sale inspection? It allows the seller to fix things that might come up in the buyer's home inspection, so there will be fewer "surprises" and hopefully less expense or price adjustment following the buyer's inspection.
But what are the disadvantages? If you choose not to make repairs that you have been informed should be made, in most states you're required to disclose that. Maybe your hot water heater has a slight leak that you didn't notice. Or maybe the inspector noticed some flaw with the roof. Those sorts of disclosures can scare off potential buyers even before they've had a chance to fall in love with your home. And remember: You are required to disclose (in states that require disclosure), as is your agent.
Also, recognize that, as a practical matter, home inspectors are going to find things wrong. Sometimes they're legitimate. But even a seemingly perfect, pristine home is likely to end up with a list of items discovered by the inspector. Maybe the items will be small (window missing a screen, or a door handle missing a screw). But sometimes they'll be big though not serious: HVAC nearing end of predicted life. Sure, the HVAC could die tomorrow or it could last another 15 years. Right now it's doing fine. But there are likely to be a few biggies on the inspector's list no matter how much you've worked to eliminate problems.
Beyond that, suppose you have an inspection done, find a few things, and correct them all. Then your agent proudly includes the inspection in the package for buyers. How much credence do you think buyers will give to an inspection paid for by the seller? Not much. They'll figure that the inspector came up with a report to make the house look good, or at least might have "overlooked" a few major things. I'm not saying that's what inspectors do; what I'm saying is that the buyers may come to that conclusion and therefore pay little or no attention to the report.
So, there are enough drawbacks to think twice about having a pre-sale inspection done.
Again, practices vary geographically. And if a couple of experienced agents advise you to do it, then definitely do it. But I know plenty of good, experienced agents who would discourage their sellers from having a pre-inspection report done.