I have a 2004 Chevy Malibu. Mechanic replaced the starter. Two hours later, wouldn't start. Told the starter was bad and it fried the ignition switch. They replaced the starter again and the ignition switch. I have had it back for 2 days and it won't start again. Should they be looking for some other problem?
A defective starter can't damage the ignition switch. There is a relay in between them and even that is not likely to get damaged. What they might be looking for depends on how you describe the problem. Unless they hear the symptoms themselves, "doesn't start" can mean lots of different things, just like "I'm in pain" doesn't tell you much.
If the problem is intermittent and hard to duplicate, you can best help in the diagnosis by making as many observations as possible. Turn on the head lights or open the door and watch the dome light. Do they dim just a little, not at all, or go completely off when you try to start the engine? Before you try to start it, does the radio play properly, power windows work, things like that. Do you hear a light click from under the hood when you try to start the engine? How about a single rather loud clunk each time you turn the ignition switch to "crank"?
Keep in mind all of those suggestions pertain to a starter motor that will not crank the engine. If it DOES spin the engine but the engine doesn't run, that is also called a no-start condition but the symptoms are totally different.
If they were working with the starter motor, my guess is it wasn't cranking the engine. Based on the repeat nature of the problem, I'd suspect a problem with one of the battery cables or connections. GM doesn't have a real lot of starter motor trouble, and the chances of the replacement being defective isn't too likely either.
A more common problem is the neutral safety switch. When it doesn't start, try shifting to neutral instead of park, and try it again. If moving it between neutral and park a few times makes it work, it's almost certain that is the problem. They are often intermittent before they fail completely.