You can bet your bottom dollar most of the workers at Best Buy have never SEEN a 5 1/4" floppy disk since they were in diapers. Most were dumped onto the Goodwill front door when they were in elementary school. And the IBM PC didn't come out until 1980, so anything else around or before that time using that size floppy would be basically unreadable by any other system (though I recall seeing a program on a Kaypro II that would read about 25-35 different CP/M disk formats (5 1/4" only, I didn't hear of anyone hooking an 8" drive to a Kaypro, though it was probably possible). Some drives CAN read other "proprietary" formats such as the Apple ][ or the Tandy - at least these ARE documented (though perhaps they intentionally weren't at the time they came out, I suspect all disk/file formats were eventually reverse-engineered. I've seen very detailed info on the Apple ][ format. It's an amazing story: Wozniak, not knowing any better, put much of the "disk controller" functionality in software, saving money over other disk drive interfaces), and sometimes a drive controller can be reprogrammed to read another file format. Worst case, a old computer freak person offering a conversion service would have a computer that wrote and read the format, and could do a serial port binary transfer to a modern computer to burn a CD on.
And even with "IBM PC Format 5 1/4" floppy" you've got the original 160k/180k/320k/360k formats, then the 1.2 meg IBM AT format (I still got one of those AT drives in a 200Mhz Pentium machine) that if you used that drive to WRITE to a 360k or lower-formatted disk, the track width it writes is smaller than the original drive, which then wouldn't read the floppy anymore. Semi-compatibility is one of life's little complications...
But MAYBE the Best-Buy manager is an old crusty person (kinda like me) who is old enough to remember USING 5 1/4" floppies, and just happens to have heard something about "format conversion" services, and could refer your character.
And the same guy who does this service (he can even read those 8" CP/M floppies, though I recall there were some proprietary microcomputer OS's that used those too. (Polymorphic Systems comes to mind, the computer store I worked at in college sold one to a writer who had a helluva time with computers with at least one "it ate my novel" story, but in spite of it managed to write and publish "Sharky's Machine"). And those 8" floppies were originally made by IBM for mainframes!), well...
Where was I? Oh, that same guy can convert your old BETA videocassette to any format you want: "Whatcha want it on? Old-fashioned DVD, HD-DVD (R.I.P), Blu-Ray, CD-video, mpeg on a CD or DVD data disc, VHS, U-Matic?" He might even be a freak and have one of the original Ampex videotape recorders first used by the TV networks, and can play back "original" copies of The Ed Sullivan Show.
Sorry you asked yet? I haven't even mentioned LP's, 45's 8-tracks, 78's, acetates (usually the brand is "AudioDisc"), nor Edison cylinders. I have the equipment to play back most of those...
Ben, your technical blast from the past...