An auction contract exchanges when the hammer falls. The deposit is committed at that moment and completion is usually 28 days later, which is shorter than most lenders' ordinary process and considerably shorter than a valuation, a legal pack review and an offer comfortably allow.
That is the whole problem. The finance is not unusually complicated; the timetable is. Missing completion does not simply unwind the purchase, it forfeits the deposit and can leave you liable for the shortfall if the lot is resold for less.
The work that makes an auction purchase safe happens before the auction, not after. The legal pack, the title, the tenancies and the condition all need reading while you can still walk away, and the funding needs to be agreed in principle against that specific lot rather than against a general appetite to lend.
Terms agreed before you bid
We take the lot to lenders ahead of the auction so the answer, the number and the conditions are known before the hammer falls rather than discovered afterwards.
The legal pack read as a lender will read it
Short leases, absent title guarantee, unusual covenants and sitting tenants are all priced or declined by lenders, and all sit in the pack you can read for free days beforehand.
Valuation instructed on day one
The valuation is the long pole in a 28 day timetable. Instructing it the morning after the auction, sometimes before, is what keeps the completion date real.
A defined exit from the outset
Auction finance is short-dated by design. Whether the exit is a sale, a refinance to term or a refurbishment and then either, it needs to be credible at the point you borrow, not worked out later.