This is a basic customer card:
As you can see there is a "Salesperson" linked to the customer, but in many situations customers can have multiple salespersons.
In this field I can only select one salesperson.
The problem created by this situation in the company is that sales people can't find customers that are not linked to them.
How can I assign multiple salesperson to customers?
If your salespeople are in fixed groups e.g. person A and B handle the same group of customers and C and D handle another group of customers, you could use the Responsibility Center feature.
Create a Responsibility Center for each group of customers and assign it to those customers. Then set the Sales Resp. Ctr. Filter on the User Setup for each Salesperson.
Using this field, obviously, you can't. You need to use some other field like department or customer group I don't know. Or if I remember correctly the was a table like ’My Customers’ where every user can build a list of customers he's interested in.
