Buying a co-op with all cash

Probably not. They'll have gift taxes after the exempt amount. High risk of board turn down.

I've helped with quite a few co-op purchases for my buyers where parents pitch in and by far the best method is for your family to deposit the full amount of the purchases at least a month prior to the board package supporting statement. That way you document the necessary amount along with the gift letter.

The separate checks method can work but can be confusing. I'd make sure your broker writes a clear letter summarizing where the amounts will come from. Specify your post closing liquidity. It can help also if you have securities that haven't been liquidated that will show enough money to cover maintenance payments.

Gift tax hasn't been an issue in my experience.

gift tax never is until you get audited ;=)

As snezanc says the board will want to be confident it's really a gift rather than a loan, in order to be confident you will be financially stable after buying. They may also want the transaction to be clear that only you are the owner (approved tenant-shareholder) and occupant, that it's not a 'partnership' type arrangement where each contributor owns, or feels they own. a share of the unit.

The seller may be most interested in seeing it in your bank account, to be confident you can close the deal.

Gift tax is between you, the gift-givers and the IRS, not likely to be an issue for the board or seller. And just to be clear it's likely a gift of this size has to be documented for the IRS, but in most people's situations it would probably just reduce the lifetime exemption (which is also the estate inheritance exemption) and no actual tax payment would be required.