How to determine how much typein traffic a domain gets?

I am in the market of aquiring expired domains and am wondering which methods there are of determining the estimated type-in traffic that a particular domain would receive. I use google keyword tool for one and type in the domain and its extension as a way to roughly guage how much traffic it will get but it seems to only give you a very rough estimate as i have aquired certain domains that would appear to get a lot of type in traffic judging from google keyword tool results but would in fact get next to no type in traffic after i aquired them (wasted investment)

Any thoughts?

The only fool proof way would be to register the domain and find out. Or you could just roughly guess by using the GMS (Global Monthly Searches) data and estimating how much would type-in the domain instead of using search engine.

There is hardly any "typein traffic" domains that expire which are either deleted or auctioned off anymore. The registrar itself in most cases keeps the domain for themselves --- they renew it and push it to their own portfolio

Don't think there's a method with even a reasonable degree of certainty for what you desire. You could try something like http://www.checkpagerank.net/google_pagerank_domains but it's not exactly what you want, although it should be a valuable asset in your line of work.