Dealing with Third Party vendors

Some advice when dealing with third party suppliers - figure out who you are working with.  If your contacts are honest, treat them well and they will treat you well.  If they aren't honest, nail them down and change them out for someone who is.  Sticking with a dishonest supplier is likely to cause issues, but realize that the problem might just be your contact and not the supplier

How do you deal with an honest supplier? 

First advice is the old saying, "good fences make good neighbors".  If you want to keep the relationship clean, you need to set and agree where the bounds of responsibilities are.  One of the worst things to your relationship will be having an issue where the responsibilities are unclear between you and then, and you both wind up distrusting the other person because you think the other is trying to pull a fast one or refuses to do their job.

Second advice, when you are in hard times with them, it helps to have contact outside of work.  Going to the pub, having coffee, the occasional meal is good to have so that you can let off steam and clarify things where you aren't being watched, recorded, or your job is not on the line.  If you want to navigate the business hurdles, it helps for you to have a friend in your contact on the other side of the business, and in unofficial capacities they will be able to explain the difficulties in ways that you do not.  This can be helpful when working through issues where responsibilities aren't clear.

Third advice: treat the supplier with respect.  If you cease to show them respect, you will lose their trust and their willingness to help you out where there is ambiguity will vanish.  That helpfulness is one of the most valuable items you can have in a supplier because it helps you to succeed where there are exceptions in your business.

What do you do with a dishonest supplier?  Get your contracts and legal departments to nail down the suppliers agreements in detail, and then hold them to it ruthlessly.  That is the only way to get someone dishonest to deliver - make it harder and more painful to be dishonest than it is to deliver on the agreements.  On the side, work to change out the supplier or the contacts if you know that it is your interface and not the company itself - it's wise to be honest with the suppliers management and explain to them what you are finding in your contacts and give them a chance to resolve the issue before removing them, because it's generally expensive to change out suppliers mid-agreement.