I’m guessing that buying from an auction means you skip all conveyancing, so any legal issues, land disputes, planning and building regs violations, sewer issues, gas, electric services etc are all unknown risks.
There would have to be a heavy discount on the price to offset those risks
that's not strictly true, I have bought many properties from auctions, it depends on the quality of the legal pack which surprisingly is part of the contract for sale, if their is an error in that pack then you can reject the property within the completion terms ie 30 days. In general I have found legal packs to be much better than the disclosure after agreement that happens with the more traditional sale.
Most auction houses return deposits if a legal pack is materially incorrect, we pulled out of a sale when the beneficial owner was disguised, person x said they owned it, but in fact a company owned it of which they were a director.
Auction houses that don't are very few and far between, there is one in Wales that has a buy on the hammer but all their stuff is at the really cheap end and you are buying a plot rather than a house and even they tell you up front you are just buying the title.
Personally I would just do the maths, if you can buy a house at say 25% under market for being un mortgageable and it costs 15% to make it mortgageable then there is a 10% profit baked in.. some of that profit will be lost due to higher finance costs initially but that shoves the onus on you to get it sorted.
There are all sorts of finance out there...and all sorts of agreements.. Hanson do a split ownership arrangement whereby they lend and 50% of the property becomes theirs which you buy back at market rate once it can be lended on. Interest on that is Bank base rate plus 2%.
It all depends on how much risk you want... plenty take on more risky stuff then just do a gut then flog on, you would be amazed what a manky s hole cleaned up and made ready for rework goes for. A set of three terraced house we tracked un loved and uninhabited in Ebba vale sold for 54k, after a demolish and planing sold for 472k as a plot with full planning for 5 houses. Total cost were probably in the region of 100k including purchase.