How do I know if my clothes are clean?

The thing that I would do is to start the washing machine again from the beginning without any kind of cleaner in it just the washing that way it will feel better and it will not be a problem if its been washed or not.

I have had to do this a few times myself.

Run them again without soap, And dry. They need rinsed and spun.

If you have the time to wash your clothes again - and be there until the end - and you can afford the expenses for a new wash, wash them again. 

Do not bother with any “laboratory” checks or tests!

Just let it pick up where it left off and complete its cycle. If you can't, wash them again. Simples.

It is not rocket science. Just wash the clothes again. Oh My God. :/ Yours is another good argument for keeping it analog, as opposed to all this digital junk

Run them through a complete cycle again.

Simply wash them again from the beginning of the cycle.

if they smell bad, then probably not... i cant think of any other way of telling

I'd wash them again, just to be sure.

If they smell like the washing up liquid they're probably clean. Probably. :D