Hi,
as long as the credentials of the client match with a user account on the server, this account will be used for login. If not and the guest account is enabled, the guest account will be used. If this is also not the case, you may be asked for credentials (exact behavior may also depend from the client OS).
You can try also to map a network drive with the net use command and add the wanted credentials within that command.
net use x: \\server\sharename /user:server\username passwort
Instead of a password in clear text you can also use the * sign, which will ask for the password.
Best greetings from Germany
Olaf