If you work for a company as a salesman, you would perform better if you think that you were a sales agent rather than a sales employee.
As a sales agent, you are dealing with both seller and buyer. You are negotiating with both parties in order to get the sales done. You do not feel the seller should have the obligation to support you. When something goes wrong, you will be patient to deal with it.
On the other hand, if you think yourself as a sales employee, you expect the management should always give you a full support to you so that you can compete in the market. When you do not get what you expected from the management, you would easily lost your motivation.
For example, when your account department is blocking the delivery due to some small payment issue. The small payment issue could be insufficient invoice and the customer side can not issue the cheque. Your account side sees the overdue payment and does not allow the delivery.
If you think yourself as a sales agent, you will negotiate with both parties. You would approach the customer and find out the soonest the cheque could be ready, perhaps you would ask for email confirmation from the customer side. After that you would negotiate the seller, showing all the payment history, and the commitment from the customer on this payment.
If you think yourself as a sales employee, you would start blaming all the supporting staff for not getting the problem solved. You would be lack of initiative and let the supporting staff to sort it out. When things go to the wrong way, you could be upset and think to work for other employer.
Based on the above example, it would be better if you can always think yourself as a sales agent.