I think that it is quite clear from the tone of what Austen as ON says that the gossip was wildly exaggerated - that Wickham from being an "angel of light" was now suddenly in the opinion of Meryton's gossips a "bad guy" and a real monster - it is a clear indication of how silly gossipy people are often inclined to change their opinions wildly.. and ELizabeth clearly indicates that she does not beleive half of what is said....

Problaby Wickham left town owing some money to tradesmen, but they had problably originally written it off as not abnormal gentry behavour from young and wild men of that class... and Meryton's genty would problaby have not seen it as all that extraordinary either....not admirable but common enough...
and he was problaby flirtatious with tradesmen's daughters, but when the word came out that he'd actually run off iwth a young lady, gossip suddenly stated that he had seduced all these young women as well.
Elizabeth now realises that Wickham is most definitely not a wronged and honest man, that he's selfish, mercenary and at teh very least overflirtatious if not rakish -and given her sister's lack of dowry, she knows that for a man like Wickham is not going ot marry an almost penniless girl who has been silly enough to let him seduce her before marriage.. He's going to hold out for a girl with some money....so her sister's ruin IS pretty certain....