The only 100% solution is “Be prepared”,
Overall, this is always…always going to have the potential of happening. Eg: Their device wont play in my system.
Indeed it’s had the potential of happening since vinyl records could get scratched or warped. The CD era yielded similar issues with some of the earlier CDRs that people would bring up to the DJ, not being readable/playable on different brands of players. CDRs burnt at slower speeds would sometimes be the only way of getting any sort of multi-player compatibility.
There’s also a current “game” doing the rounds of guests coming up to DJs at weddings, asking the DJ to play a track off of the guests MP3 player/iPod/smartphone using the headphone socket, then, after the track is played, the guest collects their device from the DJ and claims that the DJ broke their device as it doesnt do x or y or z anymore.
More and more usb datasticks are appearing in retailers with factory-fitted data encryption (Data Vault / Secure Traveller and more) which deviate from standard formatting.
In such situations, where playback of a particular track, such as bride & grooms first dance, or processional/recessional/signing tracks, I would always point the client to a dropbox account, or meet them personally several days, or in the case of weddings, several months prior to the event.