This feels like it should be quite simple, but I'm really struggling...

I have a list of quotes all made by my salespeople, each one submits quotes
for selling items to customers, sometimes the same customer will ask for
quotes on 10 or 15 different items.

for example, Fred has quoted a price (to Builders Inc) for bricks, another
price for tiles, and another price for concrete, all for the same customer.

These three items show up as three separate lines in my list, but each one
of these three lines has the same customer name on it

Fred has also quoted for other people and other sales people might have also
quoted for stuff for 'Builders Inc' too

So here's waht I'm after...
I want a table of all my sales people, and next to each sales persons name,
I just want the number of DIFFERENT customers they've quoted to, so for
Fred, 'Builders Inc' must only show as one (even though it appears three
times). I want a total number of unique customes that each sales person has
had dealings with.

I hope that makes sense

Thank you

M