Can I stop my junior staff from seeing my supplier costs and profit in the travel agency software?

Yes, in most cases you can. Travel agency software normally works on staff roles, so you decide what each login is allowed to see and do. A role for junior staff can be set to show only the selling price the customer pays, while the net cost from the supplier and the profit on the booking stay visible to you and to anyone else you choose.

How far this goes depends on your plan and on how your portal is set up. Usually you can also control who is allowed to change markup settings, who can cancel a booking or process a refund, and who can open the reports that show earnings across the whole agency. Some setups give you one role for all staff, others let you build a separate role for each person, so it is worth asking what level of detail is available before you promise a team member a particular kind of access.

One thing to watch is paperwork that arrives from outside the software. Supplier confirmation emails, voucher copies and some documents issued by the airline or hotel can show the amount the supplier charged, and your own system cannot edit those. If your staff forward supplier messages or work from a shared mailbox, they may see cost information even when the screens in the software hide it, so your mailbox access needs the same thought as your logins.

Before you hand anything over, create a test login with the role you intend to give your staff, sign in as that user and walk through a search, a booking and the reports to confirm that nothing you want kept private appears on screen.