Almost every off-market seller or intermediary will ask you to show you can perform. It is worth understanding what is being asked and why, because it is straightforward to satisfy and it removes the most common source of delay.
What is actually being tested
Not your wealth. The question is narrower: can this specific buyer complete this specific purchase on the timeline discussed?
A seller who has chosen certainty over price is exposed if the buyer cannot close. Proof of funds is how that risk gets checked before anyone commits.
What counts
A recent bank or brokerage statement showing liquid funds at or above the purchase price. A letter from a hard money lender confirming approval and stated limits. A line of credit statement. If you buy through an entity, a statement in that entity's name.
Redacting account numbers is fine and sensible. The balance, the institution and the date are what matter.
What does not count
A pre-qualification for a conventional mortgage generally will not help, because most off-market inventory is in a condition conventional lenders will not finance.
Nor will an unsupported statement of net worth, or equity in property you have not yet liquidated. The question is about funds available now.
Have it ready in advance
The buyers who move fastest keep a current statement to hand and refresh it monthly. When something fits, they are not spending two days requesting a document from their bank.
On our application, uploading proof of funds is optional — but it materially speeds up approval, because it answers the main question we are assessing.