It's unlikely you will find anything worthwhile at Flippa.
I was buying and selling domain names over 15 years ago, and the difficulty level has increased since then. Buying "dropped" domain names is also quite different now. But, I do still have some success these days and I'll share with you some tips...
Two things, this method of making money can be time consuming and involve money up front without selling the domain name for a year+. This can be okay as a side-income earner.
Buying anything off of forums/ebay/flippa/etc. is probably a no-go. Most are being sold by someone trying to profit already.
Search in places like:
NameSilo Marketplace
GoDaddy Auctions
Sedo.com (Rare, but including it. Sometimes a gem domain is posted under-valued but it's very difficult to find.)
Doing advanced searches in these places you may find a domain that was expired or has been forgotten about.
There are -so- many domain search styles I couldn't possibly go into them all. But, some try to find short domains, keyword rich domains, 2 word names, trending topics, or even finding a business that already exists and buying TheirBusiness.com and then offering to sell it to them for $xxx.
Good luck.