There are several options for the user to enter the dates and other criteria. Show Custom Dialog is easiest to script in most respects, but if you use New Window, you can pop up a small floating window where the date fields have pop up calendar controls and a field for salesperson can be formatted with a value list of sales personnel. The basic script will be the same, so I will set up a simplified version with show custom dialog as a starting point.
First, define one more global field for SalesPerson. I'll name these fields: Globals::BeginDate, Globals::EndDate, Globals::SalesPerson.
This script also assumes that you have FileMaker 12. If you have an older version, the script will need some changes as Show Custom Dialog in older versions only commits data from input fields if button 1 is clicked.
Set Field [Globals::BeginDate ; "" ]
Set Field [Globals::EndDate ; "" ]
Set Field [Globals::SalesPerson ; "" ]
Show Custom Dialog [ "Enter Date Range:" ] // Specify BeginDate and EndDate as the input fields.
If [Get ( LastMessageChoice ) = 2 // "S Person" clicked ]
Show Custom Dialog [ "Enter SalesPerson' ] // Specify Globals::SalesPerson as input field.
Else If [ Get ( LastMessageChoice ) = 3 // Cancel clicked ]
Exit Script 
Go to Layout [Report layout]
Enter Find Mode  //clear the pause check box
Set Field [ YourTable::indentDate ; Globals::BeginDate & "..." & Globals::EndDate ]
Set Field [ YourTable::SalesPerson ; Globals::SalesPerson ]
Set Error Capture [on]
Perform Find 
Sort [no dialog ; Restore ]