Only popular keywords with some kind of professional or pro branding context sell in .pro at the moment. These are the sort of checks I run when appraising a .pro.
1) Go to DomainTools.com and check the Sales History page. All it lists for Ritual is RelaxingRituals.net at $99 and Rituals.fr for 150 Euros. To put this into context, when I was buying and registering .pros in 2007, I was looking for keywords with $1m+ sales, at least 3 pages of previous sales, and multiple exact keyword sales for $1k+ in other alternative extensions.
2) To gauge the association between the keyword and .pro, put "RitualPro" into Google with the quote marks. I get 27 results, you should be aiming for 10,000-1,000,000.
3) Go to Sedo and check the keyword to see how many people have bid on domains with that exact keyword. I can find 5 bids for Ritual.de. This is OK but I would want more than 1 domain out of the 16 exact match Ritual domains listed to have bids on. .de is more popular and well known than .pro and somebody may have listed the domain at a very low price to fish for bids before listing it at 5,000 Euros.