The buyer offers less once they arrive. Can I say no?

Can I refuse a new price at the door?

Yes. You do not have to accept a lower figure because they have parked outside, or because the sofa is already in the hall.

Say no, and keep the item. If you want to accept a different price, say the new number clearly before any money moves. Read how to sell furniture locally.

What should we agree before they travel?

Write the price, what is included, and who is lifting. Ask them to confirm on the day.

A fault you already described is not a new reason to cut the price. A fault you hid is a different problem. Let them inspect, then decide. Use selling locally without cash so the payment is not a handful of notes on the step.

What if the checkout price is already paid?

On SilentSale® the amount at checkout is the order. Stripe holds the funds until pickup is completed. A different price is not a cash discount beside the app.

Cancel in the app before the PIN is entered if you both want to stop. The buyer is refunded in full. Then make a new order at the price you both accept. After the PIN is entered, voluntary cancellation is no longer available, and there is no dispute window. Read how PIN Pickup works.

SilentSale® Terms: payment is processed through Stripe when the buyer confirms checkout (section 10A.2.1). Stripe holds the funds until the item is delivered or collected (section 10A.2.2). SilentSale® does not directly hold the funds (section 4.1.4). Funds are not released to the seller until pickup is completed (section 10A.2.4). After checkout the buyer is issued a 6-digit PIN (section 7.5.2). The buyer must inspect the item before handing that PIN to the seller (section 7.5.3). The seller enters it in the app (section 7.5.4). Entering the PIN is acceptance, the order is then complete, and no dispute window applies (sections 7.5.5, 7.5.6, 15.2.3 and 10A.7.3). Source

SilentSale® Terms section 10A.5.3: a buyer may cancel a PIN Pickup order in the app until the acceptance PIN has been entered, and is then refunded in full. Section 10A.5.5: once the seller has entered the PIN, voluntary cancellation in the app is no longer available. Source

What if they say the van cost them extra?

A van they chose is their cost unless you agreed to share it before they hired it. It is not an automatic cut to your price.

You can still say no and let them leave. Compare a recorded price with a thread on Facebook Marketplace.