Samba between 2 ubuntu systems is one-way only

The HowTo you followed said that this share definition allows guest access:

[Anonymous]
    force user = nobody
    path = /home/gorfanidis/share_testing
    read only = No

It does the opposite.

To make it guest accessible and to make sure there are no Linux permissions issues I would suggest the following changes:

[Anonymous]
    force user = gorfanidis
    path = /home/gorfanidis/share_testing
    read only = No
    guest ok = yes

ok this seems to work. But it's a step back from making it work automatically from Files (nautilus). Is there a way to achieve this?

If this is a single user system what you could do is add force user = gorfanidis to the [global] section of smb.conf - right under workgroup = WORKGROUP is where I would put it. Then it would apply to all shares you create regardless of how you create them.