Take care when acquiring secondhand
I am probably the wrong person to be writing this, because I have to be honest and say I have acquired much equipment over the years and never sterilised it as a precaution against disease. I am not suggesting others don't sterilise - I have absolutely no problem with anybody else doing it, especially if it helps to concentrate their minds. I think it is sensible to take reasonable precautions, even though there may sometimes appear to be little danger. It is better to assume that all used equipment is a potential danger. You don't know where the previous owner acquired the equipment and it may have been stored for some time without coming into contact with bees. We know that foul brood will stay viable for a long time.
If you acquire from someone who is known to you there shouldn't be a problem, especially if they have live bees and haven't recently lost many colonies. The local Bee Inspector will probably welcome a call from you and may do an inspection of bees to check for foul brood. Although you should always be careful, it would be wise to be extra cautious if acquiring from someone you don't know. Don't be frightened to contact the Bee Inspector in the area where the equipment is coming from. They are very helpful and don't wish to see disease spread, although don't expect them to divulge sensitive information - they are not allowed to, so please respect their position.
Live bees are the safest as they should show up any visible signs of disease. Check for foul brood and if you aren't able to recognise it yourself, then consult the Bee Inspector. If any colony is infected it would be sensible to ask the Bee Inspector to help and advise you on how to sterilise the associated equipment if you wish to go ahead with the acquisition. I see no reason why you shouldn't, as the Bee Inspectors are trained to eradicate disease and make equipment safe. They are always keen to teach beekeepers, especially beginners.
There is useful information on the Beebase/NBU website on sterilising equipment. I refer you to that, as it will be kept up to date, where this page may not.
When acquiring secondhand equipment, unless you have been given it, it would pay to inspect it well to make sure it is in good order and assembled correctly. I have been the auctioneer at the West Sussex BKA auction for about 20 years and have seen a lot of beekeeping equipment change hands. Most of it is sound, but some isn't. I always reckon the price of commercially made equipment secondhand in good condition is around 50% of new catalogue price and 25% if it is in poor condition or home made. Very often equipment can look a bit old, but is perfectly sound or easily repairable. I have some hives myself that are well over 50 years old and still sound. They have been looked after well. I know a family of commercial beekeepers who still have many hive parts that are also well over 50 years old. Bearing in mind how much use they get it shows how long their useful life should be.
Hive parts will last a lot longer if they are repaired as soon as a problem appears. Cleaning is important and I scrape all wax and propolis off and use a stiff wire brush inside and out. This will be the time to flame out if you wish. Nail any parts that require it. I prefer galvanised nails and to prevent the wood splitting I blunt the point of the nail by hitting it on the end with a hammer - the old tricks are the best! Repairing is much easier when the parts are dry.