I travel 10+ times per year with tons of gear, while I've had some terrible experiences that have left me feeling completely f'd over, I feel like I've gotten it down to a pretty good process. Here's my tips.
1) know your airline's baggage policies as it relates to kite/surf. Find the area on their website with weights and rates, print off a hard copy and bring with you. Sometimes the agent has not idea and just tries to ruin you.
2) Weigh your gear before you get to the airport. If limit is 23kg, be under it, note 23.5, 24+, etc, but under 23. Get a small travel hand scale for your return flight. Example: www.mysticboarding.com/products/wind/ba ... lor_f8fcfb
(Probably most important piece of gear I travel with)
3) Compression bags, etc are lighter than normal kite bags, so use them. saves about .5kg per kite.
4) If you agree with tip #1, don't be an a-hole. Accept the rates and pay them. Pre-pay it online before you get to the airport as there's often a discount for paying on-line, and likely less stress w the check in staff.
5) Life's short. Unless the second bag is insanely expensive, live a little and check in 2 bags. Nothing worse getting skunked on a trip, when you could have ridden if you brought a foil, bigger kite, etc. or didn't bring your little kite. My move right now is typically all boards, foils, etc in a wheeled travel bag. 2 Surfies and foil gear with a few other odds an ends is pretty close to the 23kg limit. Then a light duffle style bag with all kites and the rest of the gear in another bag then I've got everything I need in 2 pieces. Follow the rules above and for most airlines the second bag is a manageable fee, especially as you've already checked in one as oversized, or as a surfboard and paid the fee. Having said that, I'm usually travelling for work (to some extent) so have a bunch of samples, and I'm usually going somewhere with some choice of airline and can get on one with reasonable, or at lease consistent.
6) A complete wild card is changing airlines and/or transferring from international to domestic flights and/or terminals. Basically anytime you have to physically see/pick up/transfer your baggage you're at risk of an airline double down and further ravishing. All off the above rules still apply, but again, know the rules. If you believe you've paid to have your bags checked all the way through to final destination, have some documentation on this. Tam in Sao Paulo had a nice scam running on this when I used to travel to Cumbuco via Sao Paulo.
I could add a 1000 words with stories of times airlines have completely screwed me, but more often that not if I stick to the above, it's a known cost when I get to the airport and something I can live with.