go to
www.umdgen.com
Download it, open your ISO with it and do a Dummy search.
After that I would go to PSP_GAME\SYSDIR and check if the "UPDATE" folder is there and if "BOOT.BIN" is there. If both of those files are present, you have yourself a full ISO. If they aren't, they're bullshitting you and you most likely have a rip.
note: I recommend deleteing the update folder and boot.bin as they are useless space, they don't do anything lol.
Since people *LOVE* ripping tons of shit out though, I can see why you would like to know if your ISO is full.