I want to sell art at a vendor fair, how do I do this in quickbooks? Do I have to put all my paintings in products?

I'm here to help you set up the product and service items you buy and sell in QuickBooks Online.

• Inventory. Products you buy and/or sell and that you track quantities of.
• Non-inventory. Products you buy or sell but don’t need to track quantities of, for example, nuts and bolts used in an installation.
• Service. Services that you provide to customers, for example, landscaping or tax preparation services.
• Bundle. A collection of products or services that you sell together, for example, a gift basket of fruit, cheese, and wine.

You can follow the steps below:

Add a new product or service item:

1. Go to the Sales menu, and click the Products and Services tab.
2. Click New, then select Service.
3. Add a name. If you track SKUs, enter an SKU for the product.
4.  Select the category that best describes your product or service from the Category ▼ drop-down.
5. Mark the I sell this product/service to my customer's checkbox. If you don't sell the item, you can leave it unchecked.
6. In the Sales information section, enter a description. 
7. Enter an amount in the Sales price/rate field.
8. Choose the Income account from the ▼ drop-down list and the account you want to use to track the sale.
9. Select a category from the Sales tax category drop-down list if the service is taxable or not, then click Save and Close.

For more details and steps to take: Add product and service items.

I'll add this article for future reference: Record invoice payments in QuickBooks Online.

For additional QuickBooks-related concerns, don't hesitate to post them here in the Community. We're always available and willing to lend a hand to your queries. Have a great day ahead.

@bcucksey-gmail-c 

You should record your transactions as Sales Receipt

https://quickbooks.intuit.com/learn-support/en-us/help-article/sales-receipts/create-send-sales-rece...