Car run fine in the winter, but often won't start in the summer.

YOU have to test when the problem is ongoing. With intermittent issues, you have to test then, or you can't find anything. If it wouldn't act-up on the mechanics, they wouldn't be able to find anything.

When the problem occurs, if it cranks good but won't start, have a helper crank it, while you check for spark at the plugs. If you have spark everywhere, use a gage and check fuel pressure.

With intermittent issues, you have to do testing, when problem is ongoing. To check for spark at the plugs, use a known good spark plug or spark tester, pull spark plug wire loose from plug, use tester in boot, ground metal part of tester to metal part of engine. Have helper crank while you look for spark. Unless you can tell me that spark and fuel pressure are good, when the problem is ongoing, I don't know which direction to turn. You yourself have to do the testing. Any applicable trouble codes?

Winter blend fuels can cause a problem in the summer. Change your fill-up location, see if it helps?

If you have codes, what are they? Just curious?

I told you how to check for spark at the plugs, it's easy. Some of the name brand autostores used to loan out a fuel pressure gage? It isn't hard to check fuel pressure. I can give you list of issues to check, but, you have to do the checking.