negotiating mortgage rate vs broker

Wondering if anyone can comment on their experiences negotiating a rate directly themselves versus using a mortgage broker. When we bought our house 5 years ago I used a mortgage broker and our renewal is coming up. Is it possible to get a better rate by working directly with the lenders?

Second question, can you also negotiate with a mortgage broker - i.e. ask them to buy down their rate further? This never occurred to me last time but maybe its worth considering.

Thanks,