We have lived in 4 houses during our 44 year marriage. All but the present one were uninhabitable when we bought them. The first had a stream running down the stairs when I first viewed it, it was raining, and dry rot. The second one required us to live in a caravan for 6 months - we got out of that and into the house a week before Christmas and it snowed a few days later. The third one was a repossession, all the rads had been removed and so had all the power points and light switches. I had to reinstate them all before we could get mortgage finance released. Friendly estate agent let us take a copy of the key so I could go in every night after work and at weekends to fit them, during the month between exchange and completion.
Overall it was a successful strategy - we made money and had better houses than those of friends who either bought places that had been done up to someone else's taste and standards, or new builds which even 25 years ago weren't amazing quality.
Slightly worryingly, having thought we'd got our house finished Mrs SIB announced over the weekend that she had just found a derelict house on the market locally, that we could buy and restore. Told her I wasn't keen, given that Armageddon is looming, which even she can't deny.
Buying at auction is tricky, because once the hammer comes down you have 28 days (usually) to complete the deal. So you need all your finance in place and to do that you need your costings for the renovation and to do that you need to spend some time working out what work is needed. If you aren't doing it yourself you need to make sure your contractors will be ready to start fairly soon after completion. You need your lawyers to check out the legal title and you need to have your survey done (if you think its worth it - we've never bothered with one, because we both come from building family backgrounds and were buying wrecks). So there is a lot of time and effort to be undertaken, and some cost to be incurred, all in the hope of being successful at auction, which will be totally wasted if you aren't.
Sealed bids are better - you aren't legally bound even if you are the successful bidder so you can renegotiate if things aren't as you thought they would be.
Also if the property is not your own home you will have CGT to pay when selling, assuming you make a profit. Given the economic situation, an increase in CGT rates is predictable, so its likely that net (in the pocket) profit isn't going to be anywhere near as good as in the past. Its not impossible that there will also be CGT on selling ones own home some time in the future, to help pay for the pandemic. There are political ramifications to that but all this government borrowing will have to be paid for eventually.
Lastly, I know several small builders who are finding it tricky this year with lockdowns etc and are looking at undertaking their own projects rather than working for others. If that pattern is common there is even more competition in the market.