What to do when you get nsf checks?

So I have been in business now for five going on six years. I went until May of this year before I had recieved my first bounced check. Since then I have had another one and a non payment on an job.

On that one it actually came from a closed account out of Florida, so I turned it over to St. Bernard sheriff's office and will just deduct the $95 from taxes not that big a deal (I think you can deduct non payments same as returned merchandise, maybe not...idk)

On the second one, lady was scheduled for April, she pushed it back to May. I do the job, get the check and deposit it that Friday. Comes back NSF (not closed account) So I call her and she says the repair I did failed. ( I repaired the main control on a freezer and it didn't come on before but did after I left. I can't wait around 24 hours for it to settle to temp so I had no way of knowing there was also a freon leak)
So I offer to fix the obvious freon leak FOR FREE, if she only pays the $225 she owes for the board+install.

She agrees. Well she keeps calling my office manager and rescheduling and rescheduling. This job was opened on April 3rd. I finally went back TODAY.

I get there and she is not there, teenage son let me in. I did my job, verified Freezer was getting colder and psi was perfect. I leave a bill and tell her to call with a CC (at this point I'd rather pay the 3% than deal with a check from her again).

I run the credit card.... Declined.

Now I wasn't there when I ran the card. Do I even call back or do I just call the DA at this point?
I'm going to have my office person call in the morning and re-verify the card number, maybe I wrote a number down wrong. I pretty much already wrote this job off. It's been over two months since the part was installed. I actually have $70 of my money in the repair.
I'm almost at this point not even caring about getting it, but I'm too nice a guy to want to make a case out of it. Though I know a guy who did time over bad checks, so I know it's a crime.


Third issue is even worse. I did a job for a Pita chain, and these bastards owe me $305. I didn't give them net terms the owner said "check is in the mail" on June 3rd. I have sent two certified letters since then. I did not get a bounced check or any payment. The owner is not answering his phones and a manager is never there.
I know small claims is an option, but I know they are intentionally trying to F me.
I did two repairs for them and bought the parts Next day air, and still came in well below $400 on a commercial restaurant repair (unheard of).

So how long I wait before I go in there and block the register until the owner or manager shows up.