Options:

Have command line for bot: !help, !buy, !sell, !priceof ..., etc...

******** THINGS THAT NEED TO HAVE ***********

Bot must have an in-game status: Have ... keys / Selling ... keys

Must be able to create invoice with same format and customize on the amount of keys.
Must be able to save the chatlogs with the users that it sells to. (VERY IMPORTANT, REDUCES CHARGEBACKS)
Bot will only accept keys, nothing else, and will pay the amount for each key.

*MUST NOT (YES THAT IS A NOT) AUTO ACCEPT FRIENDS, PEOPLE WILL SEND REQUEST AND I WILL ACCEPT PEOPLE*

Buy keys from someone: person sends offer with paypal address in comments, accepts trade, sends money to the address stated and then messages the person saying "thank you for selling, please leave a +rep..."

Sell keys to someone: person does !buy ... (amount of keys) paypal address, bot responds with amount of money to send, where to send and at the end contains the term and conditions again. Bot creates an invoice with the person paypal address, amount of keys, price and terms and conditions, then sends the invoice to the person. Bot sends person a message saying to check either email or paypal to pay. Person sends the money EXACTLY as stated, bot responds by checking paypal and seeing if money came in by that email, and responds to the person saying "send an offer for ... (no. of keys), please do not send more/less than amount paid or it will decline." Person sends offer and bot accepts. Then bot sends message saying to +rep.

******** POSSIBLE FEATURES (IF POSSIBLE)  ************

* Wallet system *
* Remove friends who have not bought in 14 days *