I think you're expecting way too much from him. He doesn't know that was $300 worth of clothes or a $150 scooter and even if he did at 10 that's not going to mean that much to him unless he's been raised to care about the monetary value of things. He won't be able to meet any of your expectations unless you guide him and teach him gently especially if he's never been taught to care for his things.
I agree, at 10 (to me) clothes were just something you chucked on so you could head outside and explore. The holes probably didn't bother him as much as they did you LOL. I bet even being clean is more of a grown up worry than something a 10 year old would fuss over!
And the scooter being banged up, I'm guessing he's giving it a good workout? That's not a bad thing
I completely understand you wanting him to be more careful with your childrens toys, I guess he just hasn't had much experience with delicate toys. I guess you guide him like you would your own children, and your children will help set an example for him to learn from.
Guide him, show him a good time and if he goes home with a few more manners and some great experiences then you've done well! He sounds like she's smart enough so hopefully you should be able to guide him in the right direction. Hope you enjoy your holiday with him.