I haven't the slightest idea as to how long to wait before suing some one.
I have had one lady not pay me out of hundreds and hundreds of people. She is merely banking on a scheduling mistake I made. She had used my services 2 times prior to this job and she had given me a bunch of referrals. So, I even gave her a discount for thanking her for the referrals. I was definitely a repeat customer. I gave her an estimate and she was 100% sure she wanted to do the work, but didn't know if the timing was okay. She said she'd call me.
I was scheduling about 6 weeks out at that time. So, from the time she had me out to do the bid, to the time I did the work, I forgot her stipulation. That was my mistake.
So, while we were in her tree she came home for lunch. She was surprised to see us there. And she reminded me that she didn't call me. However, she knew the work needed to be done, so she asked me if she could pay me in installments. Since, it was my mistake, I said yes. (I have never accepted such a request in the past).
So, a month went by... Nothing. A couple months... Nothing. December/Christmas time... Nothing.
I finally said this, "If you can get me one referral, that results in a job, I'll waive the cost." She thought it was fair and so did I.
Have I received a referral from her? No. Any money No.
I won't sue her over this, but I believe I would have had a case since she agreed to pay me. Did I get in writing? Na. I trusted her that her word was good enough. After all, she was a good customer...
In the future, I'll get stuff in writting. I won't be fooled twice.