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 Centerfeature.Create a Responsibility Center for each group of customers and assign it to those customers. Then set the
Sales Resp. Ctr. Filteron theUser Setupfor eachSalesperson.