Hello Marty,
There are both Non-GST and GST commissions depending on the OTA or Travel Agent you are dealing with, by rights you should probably record all income as the gross amount and then allocate the commission to the appropriate GST or Non-GST account in your book-keeping program. However often I do record the net income especially for the OTAs that pay with a virtual CC as this all goes into the system as one transaction. You of course need to check which of the OTAs are GST applicable and for any that are it is probably better to record the commission as then you have the GST offset however if there is no GST recording the net income is not a problem.
Hope this is of some help.