^ This.
I wrote
something that might help you a little, a couple years back. But I'd say that the reviews and how the seller responds inside his / her thread, are my biggest determining factors.
Do you want someone doing your SEO that doesn't speak great English, for your English-written website? I don't!
Nothing against people who aren't native to English, but for my Tier 1 links, My primary focus is on quality over quantity. A bunch of typos and grammatical errors and spun content -- YUCK! That's not quality.
Aside from this, you can get an Ahrefs account, and manually check your Tier 1 links. If the domain has no history and then all of a sudden.... BAM! 10,000 backlinks in the span of 1 month, that's probably not the best website to have a link from that points to your website. There are some exceptions, but that's a good general rule of thumb to adopt. Check the anchors of the links of our Tier 1 websites. Make sure you see some diversity. How many Referring Domains does it have? What are they? How much traffic does the website get?
Long story short, there are many variables to look at, but the good thing is that once you get a grasp on what to look for, such as what I just mentioned, you'll be able to quickly scan through all this in just a minute or two to sort of eyeball it.
