I think we looked in the phone book, and just phoned a one-man band so we could talk directly to someone who had a clue. TBH, it is more or less impossible to just look at a building and advise of state of subsidence... it is something, as you no doubt know, that is monitored over a period of time. Nonetheless, a local structural person will have had lots of exposure to this issue so should have sound advice.
IMHO you also find many houses are sold WITHOUT declarations of previous underpinning when they have had work done, so you might end up buying one anyway. I appreciate there might be legal redress in these situations, but life is short. :-) I took a view that the area is notorious for it, and my house has already been done, at great expense, and properly, so hopefully won't be subject to more movement.
I don't think our insurers are the ones who originally paid out the subsidence claim BTW, just one who had a department / person who had the authority to take a view on a particular risk (my house) and decide that if adequate documentation / consultants meant it was OK / an acceptable risk to go ahead and insure us. We are currently with Halfix Buildings Insurance and have previously used Royal and Sun Alliance.
I think my premium is amongst the lowest of anyone in the area for some reason too ! (DW is a public-sector teacher, that sometimes gets discounts, house is usually occupied etc. etc.)
I think a certain number of people are put off buying a PUP, and there are a handful of others who don't care / factor it into the price / believe it is the right house for them regardless, so yes, it might affect resale and resale value, and perhaps you should attempt to work that into your negotations ?
hth
BTW - when we were deep in trying-to-get-insurance-quote-land I came across a site specifically handling PUP insurance / advising people on this topic. Didn't bookmark it but got to it through google.