The prosecution must prove four things: that property or a right to property was taken; that this was done by deception or abuse of trust; that the taking was unlawful and uncompensated; and, critically, that the accused intended not to perform from the outset.
That last element is where most contested fraud cases are actually decided. A person who took money intending to perform and then failed — because the market moved, the counterparty defaulted, the project collapsed — has breached a contract, not committed fraud. The distinction is the difference between a civil claim and a prison sentence.
Proving intent as at the moment of the agreement, months or years afterwards, is genuinely hard. Prosecutors do it by reasoning backwards from the failure. Defending it means restoring the sequence: what the accused actually did after receiving the money, what was performed, what was paid, what documents show attempts to deliver, and what external event caused the failure.