I've delt with people like this before.
Guess what? they don't change, or grow up, or stop this type of behaviour.
It will ALWAYS be something. "Oh, I lost my job so I had to steal from you..sorry" "Oh, I got sick and my puppy died so There's a delay in me sending out what you paid for....whoopsie".
I had a guy that sold a car for me in San Diego when I moved to NM. I told him anything over 10K is yours (the car had over 70K invested). After 2 years, I said get what you can for it. He told me he sold it for 8500. I said keep the 500 and send me a check for the 8K, the wife said she wanted to see a transaction recipt, he disapeared.
3 months later, the new owners of the car tracked me down and called me asking for the pink slip, (I had no idea who the new owners were before this). I told him I neer recieved payment for the car and asked him how much he bought it for, he told me 13K.
Now, legally at this point, I could have taken the car and let him deal with the #$%*bird, but that was hardly his fault. The #$%*bird already had 3 leans against him so going after him legally would yield no results.
The wife tracked him down and called him at 0400. He gave the usually line of excuses (almost identical to the #$%*bird here) and said he'd get me my money. We gave him a timeline that he agreed to.
What he didn't know is that I had flown out to San Diego on the deadline day of payment. Needless to say, he didn't send out the payment.
What he needed was a bit of "motivation".
I got my 13K 3 days later just before I had to fly back home.
Sometimes the system doesn't work for you and more primative means are nessesary to get the results you need. People like this need to be "motivated" or it'll never happen.
If this #$%*bird sends you your tires without the proper motivation, I'll eat my hat.
In any case, I wish you luck and only regret I don't live closer to help you out with "motivating" this young indivdual.