I'm looking for advice on how to avoid baggage fees on international flights that include code shares.

Short Version:
My wife and I bought tickets from Air France. We are Delta SkyMiles Medallion members. Last week, on the first leg of our return, we flew from Catania, Italy to Rome on an Alitalia code share. At the airport, we discovered that the limit for hand luggage was 12 Kg (Ths was our fault. We didn't check the rules for Air France baggage). Alitalia told us that since we had not indicated baggage on our check-in, we needed to pay 126 Euro total for 1 bag each. Looking at the Air France website, it indicates 0 or 23 Kg for baggage allowance for Economy fares. On our itinerary on the AF website, it shows reads "1 X Accessory, 1X Hand Baggage". So how is anybody supposed to figure out what the allowance will be? After the flight, I called AF and after some wrangling and misinformation, they gave us Delta credit for the charges, based on the fact that we had SkyTeam Elite status.

I would like to hear advice on strategies to avoid being blindsided by confusing baggage policies in the future.

Longer Version:
Alitalia apparently charged us a 20% surcharge on our baggage because we didn't add baggage before arriving at the airport. The problem is that, even had we known that we needed to, the Alitalia website would now allow online check-in. Also, they ignored the fact that our tickets indicated Delta Medallion status, which should have provided free checked baggage. When I talked to Air France, the rep told me that it was my fault, because I should have known that Alitalia was the carrier for that leg and that their rules applied. The AF rep was apparently unaware that the rules state that the first leg carrier's baggage rules apply. I talked to a supervisor and read her the rule and she agreed that AF baggage policy should have applied. A good learning experience for us, but not a pleasant one.