How can my customers pay a deposit (say for 50% of an invoice's total)? I'm using QB-SE and I do not see any way for a customer to "edit amount" on an invoice.

QuickBooks Self-Employed offers a simplified invoicing feature, Info-lovingcarep.

Applying partial payments is currently unavailable. However, I can share a workaround to help you. We'll have to create a duplicate to the invoice to apply partial payments. 

You can follow these steps:

1. Go to the Invoices tab, then locate the partially paid invoice.
2. Under the Action column, click the Mark as paid drop-down arrow, then select Duplicate.
3. Open the Original Invoice.
   1. Click Add Work.
   2. Enter the unpaid balance to show the amount of the partial payment your customer made.
   3. You may enter a message to tell your customer that the remaining balance will be in a separate invoice.
   4. Click Add to Invoice, then select Send Reminder.  
   5. Select Mark as paid to record payment. 
4. Open the duplicate invoice.
   1. Click Add work.
   2. Enter the details of the partial payment made.
   3. Ensure to put a negative sign on the amount.
   4. Click Add to invoice, then select Send Invoice. 

Marking an invoice as paid will not record the payments on the Transactions page automatically. You can either record the payments manually or wait for the transaction to be downloaded automatically.

With regards to the tips, you can enter them manually. Here's how:

1. Go to the Transactions tab.
2. Click Add transaction.
3. Fill in the necessary fields, then click Save. 

I suggest reaching out to your tax advisor to help you with categorizing the customer tips.

Let me add this reference to help you with adding products and services to an invoice: Create invoices in QuickBooks Self-Employed.

We're available 24/7 if you have other invoicing questions. Don't hesitate to let us know. Take care!