Do you mean margin funding or margin trading? Have you ever used Kraken? It's definitely not the best exchange and doesn't have the best liquidity but for margin trading it is pretty well known and for the most part they are trusted.

I have never had any issues with them when depositing or trying to withdraw. The only real issue with the exchange is that liquidity is not always available and when margin trading, the rollover fees can amount to something pretty substantial depending on trade size and length of course.

Hope this helps...