I just started using QB for a handyman business. I don't sell products, but customers reimburse me for materials. Can I put this down as non-tax (e.g. $50 for TV mount)

I'm happy to help you record the reimbursement from your customer, Eric.  

We can record this as a Billable Expense added to your customer's invoice. But before proceeding, we need to turn on this function to use. Here's how:

1. Go to the Gear icon and select Account and Settings.
2. Click Expenses on the left panel.
3. On the Bills and Expenses section, click Edit pencil.
4. Turn on the following:
   • Show Items table on expense and purchase forms
   • Track expenses and items by customer.
   • Make expenses and items billable.
5. Hit Save, and click Done.

Visit this link and follow steps two and three to create a billable expense for your customer. If you want to mark this item as non-taxable, simply uncheck the tax box.

Moreover, let me share this article on running a report of your financials in QBO.

Please feel free to leave a comment if you have any further questions regarding your expenses. Take care always.