You begin by determining which bootloader version you currently have: Boot holding Power and Volume Down until you see some small text. Let go, read the text and post it. Do not use the Wipe Data option from that page with CWM installed!!!!!!!!
Next you need to find the corresponding stock recovery (same firmware version) at Droidbasement and flash it in fastboot.
That done you download the Asus firmware for your SKU, unzip that file once resulting in another zip. If the tablet boots into Android, you can copy the second zip to the root of your internal storage. You should get a notification that an update is available. Confirm it and the stock recovery will flash it. That'll put you back onto stock. But there is no way to relock the bootloader - sorry.
If that does not work there's also a way to flash the stock firmware from a microSD. Let me know.
I wrote a pretty detailed guide on flashing a recovery and rom for the TF700. It's the first sticky in the TF700 General section.
Read that for the basics on getting fastboot to work.
The TF701 is very similar to the the TF700, but there are small but important differences and I wrote that guide for people trying to get AWAY from stock, so you're gonna have to extrapolate. But the basic steps are the same.
Ask here if not sure and flash only once you are clear on each step.
An easier option would be to flash one of sbdag's stock Asus roms. You still have to determine which bootloader you have now and if your CWM version is compatible. But if both are ok, you could just flash the rom and would be on pure Asus stock, but rooted with a custom recovery and could try to sell it as such.
There may be people who actually looking for a tablet all ready for flashing custom roms to it...

Lets face it: Nobody knows what that guy did to the tablet and you should disclose that to the next buyer. So I think you have a better chance to sell it to someone who wants to tinker with it. Swappa would be a good place for that.