This is why I don't take friends or people who live on my street ~ I learned the hard way too

If your like me, this is weighing heavy on you. I think the ladies' advice is great. Just bring it up as Apples mentioned sound concerned. Acknowledge that it gets crazy in summer however could they send you the money by end of week. Either drop it off or email money transfer. Keeping it friendly and then also as a business expect payment by xxx date.
Good luck. Let us know how it goes