I subscribed to Terapeak a couple of times out of curiosity. Amazing amount of info. If you are selling one of a kind items and have no clue as to price or how rare it is and selling prices, it is very helpful.
I had some items where I was going to list at a low price and found on Terapeak that the items was selling for $25 easily as well as for $5. I listed at the higher price and sold there. Terapeak allows for up to 1 year of sales history (in 90 day blocks, only last 90 days have a link to the eBay full listing). Researching on eBay using Completed listings and Sold usually gives 15 days of history (maybe longer in some categories).
Subscription to Terapeak is expensive ($30 per month, Yearly at 50% discount if you get an offer). But using it can help get more money by listings at higher prices. If you sell enough items, you should be able to easily pay for the subscription.
Terapeak allows you to get the average selling price, % sell through, eBay categories, then look at individual listings to see the title and description for details you might be able to use.
If you know your categories and product and sell only similar things, Terapeak is most likely of no use.
