I've rejected quite a few edits in the last minutes from a user with 1 point of reputation which was substituting the posts content with a financial spam. is it really possible that a new user is allowed to go for a edit spree like that? Shouldn't it be some minimum reputation at least?
Good catch. Clearly, the user registered with the sole purpose of posting spam content and defacing posts. The profile has now been destroyed.
The way SE works is that anonymous and low-reputation (< 2k) users are allowed to suggest edits. These are placed in a queue where registered, >2k reputation users review them and decide whether or not to accept them. Therefore, there is an inherent reputation limit to edit posts. Unfortunately, this means that sometimes anonymous low-reputation users go on post-vandalising sprees and there is nothing we can do to prevent this. What we can, and should, do is reject the edits and flag the user for moderator attention, like you did.