Questions to ask broker to determine if they are ECN?

Hi,

There may well be a thread on this already but I didn't see it.

I was wondering what questions I should asking brokers to determine whether they are genuinely ECN brokers or not?

So many seem to say they are ECN brokers, but it's becoming increasingly difficult to confirm which genuinely are and which aren't.

Thanks!

Questions to ask broker to determine if they are ECN?