There's aspects of
@Tim W and
@Rod 's posts that are attractive. Although the scenario Rod has put forward is not always as cut and dry in these types of situations.
Ideally, I would want to know more - Was your friend posting these items on their own behalf or were they operating as some form of entity ie, a company? Even if not, is it common that your friend sells items online?
It's commonplace that such commercial entities may offer items for pre-sale (or through other arrangements) whilst they await to receive stock from suppliers, distributors etc. It's also common that relationships between distributors and retailers may break down, stock is lost etc. Hence a retailer not being able to fulfil order(s).
Like Tim has mentioned, much would depend on what they've been charged, what evidence there is and how much time has past between the sale and the visit from the police.
Say if the above scenario were to apply where your friend could provide proof of such arrangement and reason as to why stock was not delivered to customers and refunded the sales in full - Depending on the amount of time past, there
may be an argument for your friend's lawyer to contact the prosecution and offer up the explanation that there was never any intention to deceive and that it was all a result of a breakdown in the relationship (or whatever) between supplier and retailer (your friend) that caused your friend unable to fulfil the purchases made - Whilst also providing proof that all purchasers had received a refund when it became clear to your friend that they weren't going to be able to fulfil orders - Again, this may or may not apply to your friend - Much depends on their exact circumstances.
In contrast, purely refunding said purchases 'just because' will likely not cause the prosecuting body to just drop the charges, as an offence may have already have been committed. However, it would likely be viewed as a mitigating factor that may reduce the severity of the offence.
Your friend should retain a lawyer for advice as soon as possible.