I have been thinking about creating a Google Sheets - spreadsheet for trading that can be updated by all parties trading in real time - (In the past I have done amazing things with Excel and I feel I can transfer these skills.) Then arrange live trading sessions on Google + or even Skype. I believe in Google plus you can get multiple people on at the same time. The main reason for this I want to reposition my collection to Northern and Rural Nevada so I don't keep purchasing on Ebay.

My question to all... How to achieve a fair trade? I would like to hear your ideas

My Idea
I felt a drop down cell with 3 prices per (Low/Medium/High) per letter grade like in the Chip Rack. Then the columns will add up for both trading partners to try to equate a fair trade.

Any additional thoughts to this idea let please reply.