En Marche! was only founded within the last year. Although they attracted a considerable amount of donations, not sure we're talking about the same scale of money.
Accounts are checked after each elections by the National Commission on Campaign Accounts and Political Financing; it is an active check, as some of the previous campaigns refunds were blocked because of some wrong doing.
More details available on Wikipedia (translated from FR): https://translate.google.fr/translate?sl=fr&tl=en&js=y&prev=...
Source (in French): http://www.zdnet.fr/actualites/lection-presidentielle-l-anss...