Your best option is to be prepared to pay the fee when you check in for the return, but be polite and courteous to the agent and see if they will waive it.

I recently checked into a flight from Hong Kong to Jakarta on Garuda. The agent checking me in was going to charge me for my second bag but a supervisor who happened to be standing nearby intervened without being asked and asked me how I had arrived in Hong Kong. I said "United" and he said "do not charge for the extra bag". Garuda and United have no relationship and the tickets were purchased separately. I was actually in Hong Kong for about 16 hours between flights so I immigrated and spent the night in the adjacent hotel before checking in at Garuda the next morning.

I'm not sure what the rules are, but I wouldn't let a checked bag fee become a big issue. How much does the whole round trip cost? How much is the bag fee if you have to pay it? Perspective.