Proof of Funds for a cash offer

[Jim Sokoloff]

Suppose I'm making a cash offer (no financing contingency) on a property. Reasonable seller is going to want some kind of proof of funds. Which of the following, if any, would suffice?

1. Current bank statement showing a checking account with that amount (plus some fudge factor) in it?

2. Current brokerage statement showing an investment account with that amount (plus some margin) in it?

3. Current brokerage statement for a margin account with that amount (+ margin) of "cash available to borrow"?

4. Current HELOC statement showing available line of credit sufficient to buy the property?

It seems logical to me that all four would be equivalent (perhaps a slight nod to #1, since everyone would understand that immediately), but I wanted to ask the question of how it works in practice.

Thanks in advance.