For me it's about clan rules, & the environment you want to create.
If the name is content that you wouldn't encourage in clan chat, you can't allow it as a clan member name, as it will always be sitting there in the clan list, making it unrealistic to discourage that type of content being discussed.
As far as guests go, if it's blatant I'll just kick.
I've found it isn't worth the energy to have a discussion about it with the guest.
If they want to enquire after, I'm happy to chat about it.
If it's not too bad, I might allow them to guest for a day.
If I had any real concerns I'd make contact & discuss.
Any unresponsiveness I've learned is often game playing, & I'd then remove them & attempt to make contact via pm.
If there's any problems in an application, I'll address it then.
The application form is your best opportunity to help your clan & the prospective members to both determine if you are a good fit for each other.
I allow name changes, I don't refuse applications based on current names.
It's more about their attitude when you present them with your rules, & the reasoning if necessary.
I'm happy to explain the reasoning as a courtesy - most applicants have no idea what is required to run a clan & maintain respect between members from all over the world.
If the prospective member is happy to listen & accept, great, no drama, happy to recruit.
If it's clear they view it as more of a discussion, & essentially argue back about why your rules are stupid, I wouldn't recruit even with a name change.
If they state their views plainly, not argumentatively, and they are contrary to clan rules, but they are happy to change their name, I'll recruit them too.
I encourage discussion about anything, clan rules included, provided they show some awareness that the realities of running a clan may differ to idealism.