On Customers, keep each buyer once with a phone number and location. On Sales, log the date, the customer, the crop, the quantity and the price, and enter what they have paid; the balance owed works itself out. On Market Prices, jot the prices you see at different markets so you can compare before you sell.
An outstanding-balances view shows exactly who owes what, so a follow-up is a glance, not a guess. Yellow cells are your only inputs. The premium version prints a proper invoice and statement, and puts sales by crop and balances owed on a dashboard. Opens in Excel or Google Sheets.