Typically there is a grace period during which the registrant can still buy the domain back without paying additional fees, but the length of it varies from registrar to registrar. It could be as short as a week or two, as long as a year, or not offered at all (although reputable registrars offer a grace period). The length of the grace period also depends on the kind of top-level domain (.com, .org, .net, etc.) used.

Trust flow refers to the number of quality backlinks that a website has. If backlinks from websites that have a high domain and authority ranking point to your site; your website’s trust flow will increase. Trust flow is also measured on a scale of 1 to 100. If your website has a large number of backlinks, but they are not from trustworthy and reliable domains, your websites trust flow will be low. On the other hand, if you even have just a handful of backlinks to sites that search engines rank highly; your trust flow will increase.
Quite a lot of the time majestic trust flow will be great but ref domains below 10 but when I check ahrefs its considerably higher for ref domains. Without ahrefs I would of passed over these domains and missed out. Worthwhile addition if your building a lot of pbns. I also use linkultra backlink for my final spam check as it checks language,site type and if backlinks are comment, profile spammed etc enabling me to check if the backlinks of the domain are solid very quick.
This is a little bit on the grey hat/black hat side of the spectrum. But the fact is building a blog network with expired domains flat out works. The only issue is getting those cream of the crop domains without going broke. This video will walk you through tested strategies and techniques you can use to find powerful, yet affordable, expired domains.
It’s easier to rank higher with expired domains: Depending upon your domain age, page authority, trust flow, expired domains tend to rank really well when compared to new domains. Most new domains don’t have any DA, page authority or trust flow so it’s really harder to rank well in Google. This won’t happen with the expired domains as they are already established well and might be getting decent amount of traffic from search engines.
2) prerelease auctions.  These are domains where the auction venue has contracted with the registrar, like Fabulous or Moniker, to auction off non-renewed domains.  Just before a domain enters the pending delete process, it goes to a private auction to any person who has backordered the name.  Some people feel that back links on these type of auctions still provide a SEO benifit. My testing indicates that there is zero SEO benifit when these domains are redirected into another site.  So if you get a domain with "pink squirels" in a lot of achor text to a domain and then point it at your domain, you don't rank for "pink squirels"
Searching for a suitable domain name for your website can be quite trying. The reason for this is that the names that you want to get have already been assigned and are not available. As an SEO you know the importance of getting a domain name that describes your business as closely as possible. For example, if you are running a car rental service, you will look for a domain name that has the words ‘car’ and ‘rental’ in it. So if you can’t find a suitable name, you could use the expired domains tool which might show you domain names that would meet your requirements.

They are easy to type and remember: You can’t get a easy to remember new domain name without paying huge bucks these days. Gone are the days where you can simply grab almost any incredible domain name just by paying a couple of bucks. This is one of the major reasons most people look for expired domains because most expired domains are short and sweet.
.ac .ae .af .ag .am .ar .as .at .au .aw .ax .be .bg .bi .bj .bn .bo .br .bw .by .bz .ca .cc .ch .ci .cl .cn .co .cr .cx .cz .de .dk .dm .do .ee .es .fi .fm .fo .fr .gd .gg .gi .gl .gs .gy .hk .hn .hr .ht .hu .id .ie .il .im .in .io .iq .ir .is .it .je .jp .ke .kg .ki .kr .ky .kz .la .lc .li .lt .lu .lv .ly .ma .md .me .mg .mk .mn .ms .mu .mx .nl .nc .nf .ng .no .nu .nz .om .pe .pf .pl .pm .pr .pt .pw .qa .re .ro .rs .ru .rw .sb .sc .se .sg .sh .si .sk .sm .sn .so .st .su .sx .tc .tf .th .tl .tn .to .tr .tv .tw .ua .ug .uk .us .uy .uz .vc .wf .yt .za