you only need to pay if you remove the copyright or intend to sell the *product*.
If you're selling the service of installation, no liscence fee is necessary.
For example - fictional character Phil has a site where he posts YaBB SE for download for free, and a link to where people pay Phil $5 to install yabb se for them.
In this case, no fee is necessary.
Example two: fictional character Pat has a site where she sells yabb forums to her customers (like
xsorbit.com ) in this case, a liscence is necessary.
you ok with that?