@francis,
Well in depends based on the type of buyers.
If the buyer is a domain investor / reseller / broker , he would prefer to grab the expired ones at cheaper price so that they can sell it with profits in future.
Whereas if the buyer is the actual end user , he might first prefer new domain for his business , if its not available then he would search for expired ones that is available , even then its not available , he would contact brokers or the actual domain's owner to buy it with an lucrative offer.
When it comes to Industry , almost every business whether they belong to IT or Drop Shipping or E-Commerce , they look for promising domains .
Finding the hot industry in terms related to domain is bit hypothetical.
Also its seasonal , for example when cryptocurrencies where booming & much hyphed , domains with crypto / digital currency had a huge crush , then it slowly faded away.
Hope it helps !!