I admit I use radial cleaners for DVD's but they're not really that effective. Most of the time, the problems are scratches or defects in the pressing process that cause most read errors. Although someone brought me a disc they couldn't play and I determined it was because, apparently, someone had smeared a blob of chocolate onto the bottom! The radial cleaner worked there to fix that problem. As for what to clean a disc with, you can get various kinds of sprays, etc, but I generally use 90% isopropyl alcohol. Don't get the lesser 75%, etc. They tend to leave films behind. However, I've also employed what was suggested before by using my thumb and my shirt to clear up small smudges.
What I do to test the readability of a disc is to use ImgBurn to read it to an ISO file. It will still copy the encrypted data but I don't want a playable disc. I'm just testing the readability of it. However, this doesn't work for structurally protected discs. Another method is to simply try and copy the VIDEO_TS folder in Windows/File Explorer. Again, you don't want to get a playable VIDEO_TS, just make sure it can be read. What I used to do was put in a DVD in my PS3 and play all the contents, the movie, the special features, etc. at 10x all the way through. If the PS3 didn't encounter pauses, it was a fairly good indicator the disc was entirely readable.
I recently got in a DVD from 2020, I believe it was, Driving While Black, that was corrupt from the factory. It wouldn't play past 9 minutes into the disc. I returned it for a 2nd copy and that worked fine. It happens. Not very often, but it does.