Finalize early, when to say yes and when to walk
Vendors ask for FE because they want the money now. Buyers say yes because they are new and think being polite matters. Both of those are bad reasons to give up your only safety net.
What finalize early does
The market holds your deposit in escrow until you confirm the order arrived. If you finalize early, you release the money to the vendor before the package hits your hands. The vendor has your coins, you have a shipping label and hope. If nothing arrives, the market cannot help you because the escrow is already gone.
Default answer, no
New buyers should say no every single time. Not "let me think about it," just no. If a vendor pushes back, that is your answer about the vendor. Real vendors know FE is a big ask and either avoid asking at all or accept the no without drama.
Some markets let you say no as a default setting on your account. Turn that on. It saves you from being asked at all.
When it might be reasonable
You have used the same vendor multiple times before, with escrow, without any issues. The current order is small enough that losing it would be annoying but not painful. The vendor's dispute record is essentially clean. Their reviews from the last month are all positive. The reason for the FE ask is real (their previous market went offline, they are short of runway between shipments, they need coin for restock in a specific window). And you have already asked around on Dread or wherever, and the general sentiment is that this vendor keeps their word.
All of those, not one of those. Even then, FE is a favor you are extending, not a normal part of buying.
The tell that says walk
A new vendor asking a first time buyer to finalize early is a scam. Not "probably" a scam. It is the exact script. They put up a listing at a below market price, wait for a buyer, ask for FE citing some story, take the money, vanish. That is one of the two most common Tor market scams. The other is fake mirrors. This one is easier to avoid than that one.
If you are going to say yes anyway
Start small. Order the minimum quantity for the first FE round with that vendor. See it through. If it goes well, next time you might FE a slightly larger amount. If any single order goes wrong, they are done, do not FE with them again.
Also, screenshot the vendor asking. If it comes up in a dispute, the market moderators can see the ask. Whether that helps or not depends on the market, but it is not zero.
What vendors say to talk you into it
"I have too many disputes, escrow is killing my cash flow, please FE." Meaning either they really do (which is a sign of a bad operation) or they are lying (which is a sign of a scam). Either way, no.
"You have to FE to get the discounted price." Meaning they are pricing in the extra profit from the buyers who never see their orders. No.
"Everyone in your position FEs, only new buyers use escrow." Not true and clearly a pressure tactic. No.
"I have shipped 2000 orders, nothing has ever gone wrong." Then they can afford to wait three more days for escrow to clear. No.
Escrow is not a favor you give the vendor
It is what makes the market work at all. If you FE with every vendor, you have paid full price for a directory with no protection, and you might as well be buying off Instagram DMs. The whole reason to go through a market is the escrow layer. Do not give it away for free.