Hey, don't feel guilty in the least. It's your time too. And if you are scheduled with a particular student, and he/she no-shows, you don't make any money if you don't charge them - AND no-one else can schedule you.
Here, the first thing I do is tell my students to PLEASE CALL me if they are going to cancel - even if it's 30 minutes before the scheduled time - just call and we're square.
If they don't show and don't call 30 minutes after their scheduled time, I call them to see if they're coming.
If they're not, they get charged
Instructor Time (not for the airplane rental) for the entire time they have me blocked off.
I had a guy block me off for four hours a couple of weeks ago. He was a "hand-me-down" from another instructor who left and I had been informed that he was notorious for either being EXTREMELY late or not showing at all.
So, on our first day, we had a little chat and I explained the above policy to him and he said "cool."
Sure enough, the very next lesson = no show.
I gave it 30 minutes, called and he said in a very tired voice "Oh, I can't make it today.....let's just bump it."
I informed him that was fine, but
per the renters agreement that he signed he would have to pay for the entire 4 hours of instructor time.
He didn't like it, but I don't care. I've got a kid to feed.
Look out for #1, bro. Your time is worth $$$$. Be courtious to your students - be up front with them about the consequences of no-showing, call them if they are unreasonably late and then charge them if they no-show on you.
After all:
"It's not about the money......it's about the money."
Best of luck!
R2F