I don't know if it's legal to auction off instruction jailbreak an iPad. But there are other issues:
1. Jailbreak your device, and lose your warranty.
2. Someone who uses the jailbroken device can no longer recieve software updates, since the orignal system as been replaced.
3. It's possible that other apps will no longer work with the jailbroken device.
4. Signifcant performance slowdowns have been noted on some jailbroken devices.
5. Why would someone auction instructions for jailbreaking if the information is available, free, elsewhere?
6. Bugs, malware, and viruses can infect jailbroken device more easily.
And...
7. Posting information on jailbreaking, with links, can be construed as an advertisement for the software.