The easy way is to search for the chip using advanced search - completed items in ebay and you will get all sales for the last month. The guides may not be perfectly accurate but in most cases if you can get a chip for 50% of low guide value you are getting a fair deal. Buy the guide before buying the chip. I even have the old copies of my guides in each car for when I am out travelling. They may be four years out of date but at least I know if a chip is worth $5 or $5000.