Pretty easy to check the webpage and see if it's listed as 'closed'. If it is, honor the wishes of the owner and find somewhere else to play.
Not to rehash what I have already said but...
MYGMRS and Repeater book do NOT maintain updated listings of every machine in the USA. It's all crowd sourced.
Besides...
Who sits by their radio 24/7 chasing off "unwanted users".
A huge amount of closed and open machines in Socal and Norcal are unlisted....for a very good reason.
Want some examples?
A large linked system on 675 in Socal and Arizona is using 4 repeaters on sites in San Diego, L.A. and Yuma AZ.
Don't see that listed anywhere...open or closed?
New site on 675 on Mt.Wilson....open or closed? No listings anywhere.
700 high-site with killer coverage in SD and Riverside-San Berdo...listed?
NO open or closed...nobody answers when hailed.
I assume it's open unless you take great measures to protect it.
Why does anyone even need a private repeater on GMRS...spring for a part 90 allocation of you want less intrusions.
Besides...
Part-95 doesn't even define "private repeater" requirements or even a legal definition.
I support the "Open Repeater Imitative".
Make all of them open by default.
Ker-Chunk and WangChung tonight!