If done openly this can be useful, but the option must be explicit. You cannot rely on make-believe conditions.
Evidence was presented that Guest did no real checking on the property, he just found a better deal. Guest's website, in which he advocated using "director approval" clauses as a device to escape from contracts, was used as evidence that he merely wanted to lock up the property while he went shopping. Had the contract been written to allow the purchaser to cancel at its discretion, Arcadia would have walked away without consequence, although the vendor may not have been willing to sign on those terms.
Such loosely worded clauses are common in real-estate deals and purchasers need to be careful when signing them; if you want time to consider if the property deal is a good one, the clause needs to clearly state that you have the right to walk away with no consequences. If you sign a contract with a "due diligence" clause and do nothing, or "subject to finance" and then do not seek a loan, then congratulations, you may have just bought the property.
Guest had the last chuckle, however. After he lost in the High Court he liquidated Arcadia, leaving the successful party with only a claim in the liquidation.
The purchaser has not received a cent and is not likely to unless the liquidator takes action again Guest. Perhaps mindful of this, Guest funded litigation to take the matter to the Court of Appeal where Arcadia, in liquidation, lost.
The matter may still proceed to the Supreme Court.