Its not a trick to buy a really undervalued property, it is just blind luck and something you would not be able to repeat.
I'm not sure it's necessarily luck (overall) if they're actively seeking one... sure that they find any given individual property perhaps has a luck component but that they find a property that is undervalued and in a state of needing some work on it etc.. isn't really lucky unless those things are super rare. Auctions exist, bank foreclosures exist etc.. might find more of the latter if we do get a big economic hit after this winter.
Alos just seeking value - prices can be slow to move/adapt in property... we're potentially entering a period where increasing numbers of people will be working remotely - moving away from London say previously might have involved a strong desire to remain close to a train station with a fast train into London, these days perhaps it doesn't matter so much. Some areas will stagnatie or take a hit, others could be undervalued for some time while people adjust - there is obvious demand in the obvious areas from people moving from London at the moment (though lots of these might well be people who'd already been considering a move in the next year or two and decided to bring that forwards thanks to Covid19) the less obvious areas might still be slower to catch up and could present value.
Certainly when I bought in London I sought value - I ended up with a former BTL flat that the landlord wanted a quick sale on (due to a death - his wife had been managing the property and he didn't have anything to do with it) - I put in an offer below asking and emphasised that I was a first time buyer, deposit ready, mortgage approved and can move as quickly as the solicitors can do the paperwork... it was accepted... within months the property was easily worth a significant 5 figure sum more than I'd paid... years later I've "earned" a nice six figure sum from the rise in value... which of course can now be used as a rather fat deposit on a house outside London. (granted I might end up taking a bit of a hit on this thanks to Covid but given how much it has risen I'll still be well ahead I think).
There are of course downsides as someone else mentioned - if you lose your job or have some other significant life setback etc.. you still have that mortgage you're liable for, no just cancelling the contract in a month or two and moving home with parents for a bit etc.. It can take time to sell and is still (IMO) needlessly time consuming - process has much room for improvement (especially when the same checks get performed and lots of the form filling is just mundane and routine. You're tied to that property.
One think I should have done in hindsight (and did think of this after the brexit vote) was to buy some storage space. There have been two occasions now where I've thought that it would have been useful to sell my property and invest elsewhere - prior to brexit and at the start of this year. I decided it would be too much faff but really, if I'd owned a lock up etc.. (or just rented some self storage) then that could have been an interesting play. Probably not something you'd want to do with a family home you plan to stay in long term mind but for a generic enough apartment (granted it is a nice apartment) then meh - other apartments are available to be bought again after, at the same development too... perhaps I could have upgraded to a penthouse or perhaps I could have used it as an excuse to buy outside of London.
Anyway - for the moaners, consider a move to China?
https://global.chinadaily.com.cn/a/202009/24/WS5f6bef01a31024ad0ba7b625.html
Supported by subsidies from the provincial government, farmers can get new homes by spending 15,000 yuan ($2,205) for 36 square meters per person. For example, Li, his wife and one of their grandchildren paid 45,000 yuan for a house of 108 square meters.