An important aspect is proper communication via email or video conferences. communication can remedy many issues and also help strengthen a relationship to begin with. One thing I have noted with suppliers is ensuring that the expectations of the product ordered are very clear. Each and every vendor probably supplies to multiple different clients all with different points of view on quality. By communicating to the supplier the correct expectations in terms of supply demand and quality this can help strengthen the relationship with the supplier. Essentially, everything leads back up to the communication front and ensuring the vendors get paid in a timely manner.