I always thought that there were two distinct classes of tool thieves; at the bottom end of the scale you have the druggies who are generally pretty inept and will nick anything they can lay their hands on to finance their next fix, so that shiny new £500 drill you left in the cab of the van is probably only going to amount to a couple of three "fixes". At the other end of the scale you get the professionals like the bunch of bastards active in central Manchester in recent weeks; these guys seem to employ "spotters" on mopeds to find target vans and to warn them of the approach of the police which allows them to get on with the task of peeling down the side doors of vans and emptying them of anything of value. We've had four guys done on site in the last 10 days, all the same MO. Talking to lads on other jobs we aren't alone (they've got to pay for Crimbo somehow?)
The full-time thieves sell to professional "fences" who "de-mark" the tools and then either sit on them for a while before selling through auctions, eBay, etc or for some stuff (especially the bigger stuff) they'll pack it in a container and get it shipped out of the UK pretty quickly. This I learned the hard way a few years back when I had a workshop turned over. In that case neither the thieves nor the fence got prosecuted (the CPS dropped the case at court), but at least I had the satisfaction in learning a little while later that the "fence" had had his property (house, workshop and stock) all seized and sold by HM Customs and Excise - naughty boy hadn't registered for VAT and had no receipts so they back registered him on the basis of value of stock on hand. He also got prison time for his sins. Personally I'd have had him burned at the stake.....