As I was trying to get over, you need to be fair. Not nice. You'll have to (probably?) step outside your comfort zone and be assertive so your vendors deliver

As I was trying to get over, you need to be fair. Not nice. You'll have to (probably?) step outside your comfort zone and be assertive so your vendors deliver what you ask of them in a timely manner. You're their customer, you're not there to help them feel better or inspire them. If you're the one that signs off their timesheets/customer acceptance reports/etc then you're the guy/gal that sets the expectation for them. Be consistent with them and be firm about behaviour you don't like. Of course reward occasionally but appropriately (ie outstanding work, etc). But at the end of the day their reward is a paid invoice. As for the lawyering up, sometimes you need to, often you don't ... lawyers are there generally to avoid litigation (expensive/messy) not cause it.