In my experience you are practically expected to negotiate, 5-10% isnt unreasonable. But it is a tight market lately so ymmv. I would guess however that the higher your rental bracket, the more you can reasonably expect to shave off. Also make sure the mgmt fee or other expenses are taken care of so you're not surprised when/if the bill comes. Try to get the landlord to pay or split 50/50. Landlord should pay for the government rate though.
It really depends on whether you get a good agent or not, who can show you the places you want to see without you having to waste your time doing research on your own. You can save 1/2 a months rent (the commission) that way, but it depends if you have the time and inclination to do it yourself. Probably if you are new in town and need to secure a place fast, that would be the easiest way to go.