Finalising early (marking an order received before it actually arrives) drops your escrow protection. Once you finalise, the coin is out of the multisig contract and the vendor has it. If the item then does not arrive, there is no dispute path to reverse the release.
Why vendors ask for FE
They want the money before the shipping window closes. Some vendors have legitimate reasons (short on runway between shipments, moving between storefronts, needs to restock). Most FE requests are scams. A new vendor asking a first-time buyer to FE is a scam pattern.
The Reading Room position
Do not FE. If a vendor pushes back on the refusal, choose a different vendor. If a vendor you have used before asks you to FE for a good reason, treat it as a favour you are extending, not a normal step, and only for small orders you can afford to lose.
Escrow is what makes the market work
Give it up and you are buying on an honour system that has no dispute path. The whole reason to go through a Tor storefront is the escrow layer. Do not surrender it for free.