A genuine onion v3 address and a phishing address look superficially similar when displayed. Compare these two hypothetical addresses: anubizuvsegxjqkjlsf2l74.onion and anub1zuvsegxjqkjlsf2l74.onion. The second replaces "i" with "1", which is nearly invisible in most fonts. Users who scan addresses rather than reading character by character will miss this substitution.
Vanity generation allows scammers to create addresses that share the first 5 to 7 characters with the genuine address of a well-known service. For a 7-character vanity match, generation time on a modern GPU is measured in days - a reasonable investment for scammers targeting high-value dark web markets. The result is a phishing address that looks convincingly similar to the genuine one at first glance.
This means visual verification of .onion addresses is insufficient. Cross-referencing against verified sources is the minimum required verification, not a belt-and-suspenders addition. Never proceed with any high-value interaction on a dark web service based solely on an address received through a single unverified channel.