As a general rule convicting someone of fraud requires you somehow prove their state of mind. A person must set out to deliberately defraud someone for it to be considered fraud.
Of course proving a persons state of mind is extremely difficult. As a consequence it’s unlikely that police or prosecutors are going to take an interest in fraud that only involves small sums of money (less than a few million $).
However proving that a contract is unfulfilled is pretty trivial, and generally cut-and-dry. But failure to fulfil a contract obviously isn’t a criminal offence, so your only option is to file a civil suite. Thankfully most countries have small claims courts that cheap and very accessible, but with limits on how much you can claim. Just because the amount of money you’ve lost is above the small claims court amount, doesn’t prevent you from suing of an amount within the purview of a small claims court.
Beyond that, use a credit card. If credit card networks have provided any value in this world, it’s in the form of generally consumer friendly chargeback processes. It’s in there interest to make sure that people feel safe using their credit cards to buy stuff, more purchases means more transaction fees for them.
