It's not you or your talent, it's them. You answered your own question in the body of the post:
"I have not been paid for said cake yet and it's a week later" and
"I am not even sure if the parents liked the cake because I am sure I didnt here those exact words (or anything similar) come from either of their mouths."
Duh... If someone is going to stiff you, they are certainly NOT going to rave about your cake. By not saying anything, they have the 'out' of saying "Well...it wasn't really a very nice cake and wasn't what we wanted"
As many, many before you have learned: Do NOT, EVER, turn on the oven or buy any ingredients until you have the money. Once you have been paid, THEN buy the ingredients and turn on the oven. Betcha future cake recipients will rave about the cakes they've already paid for.
There are about 10,000 posts on here saying you can really get run over by friends and family. If you don't get paid, the friendship will never be the same--you know it, they know it. If you don't get paid, the parent's of your son's friend have ended a friendship over the cost of a cake--sad, but true.
Now, having said that and been all self-righteous and smug, I will tell you that I took my first "paid" order for a gingerbread house that took me 10 hours for a teacher at the kid's elementary that I barely knew (except to know that NOBODY likes her). I told her I'd only charge for the ingredients and supplies, and, guess what, did NOT get the money up front.
I was extremely lucky and got my money on delivery.
Basically, don't beat yourself up, honey, we're all trusting idiots.