Is it considered to be a good practice or not if I use both a keyword phrase AND its reversed keyword phrase in a domain, url and title? For example: coffee research, research coffee Will search engine treat the 2nd as a duplicate or spam?
I've seen evidence that the order of the words DOES count for SEO but you will still do alright with that domain as long as it's on .com, .net, etc. It's won't be considered as spam you just won;t get as much traffic as say "coffee research". Get some coffee related keywords into the page names such as "researchcoffee.com/strong-coffee-lovers.html"
You can do it that way, but maybe it is better to just pick one of them which is the most popular and go for that and than make another page for the other keyword.