If they don't know any better, they should just choose some relays. Maybe 2 inboxes and 3 outboxes.

I would like some trustable sources of knowledge that monitor relay capability and suggest only relays that suit for those purposes. Right now someone can easily choose an inbox relay that is paid (and that will not suit) or an outbox relay that specializes (and that will not suit either).  I've been hoping someone writes a relay tester and maintains such a list for the community -- in fact we should have competing lists. But it hasn't happened yet.

I manually went through many relays and picked 20 to suggest to new gossip users which I verified accept new users notes and serve them back out, which I recently shared here: nostr:nevent1qqstunh264x95nqvmdjt8y8h49e07fq7f4h2k4g7q3eh04htgg2yk9qpypmhxue69uhkx6r0wf6hxtndd94k2erfd3nk2u3wvdhk6w35xs6z7qgwwaehxw309ahx7uewd3hkctcpr4mhxue69uhkummnw3ez6vpj9eukz6mfdphkumn99e3k7mf0v8xg9j