Run them through
Majestic and look at the Trust Flow and Citation Flow scores to get an idea on how many backlinks the domain has, and how good of quality those backlinks are..Then, jump over to
web.archive.org and look at the previous content that was on the domain, determine if it was an actual website or something spammy. Finally, do a free domain analysis using the
Moz Domain Analysis Tool and see what spam score the domain has, and if it has any top ranking keywords.
You can always look them up on Alexa or
SimilarWeb to get an idea of traffic as well.. The steps above should help in making sure you're getting an expired domain with decent backlinks which also isn't spammy.