Address Verification is a slightly easier prospect than (for example) natural language geocoding or identity verification. Canonical street addresses are generally understood for a particular jurisdiction and many postal services keep 'common name' dictionaries as well - they've been doing this for a while, after all.
Only way to judge is to test it out. Our data comes from the local post office of every country. We have street level address verification. Happy to give you some free credits to try it yourself just email me.
We don't claim to be perfect and nobody is. Some countries have greater detail in their postal system than others do which affects accuracy. We have an internal grading system for each country we support detailing exactly how much information we have (larger/developed countries we typically have 98% coverage for street or building level). For those interested, feel free to email me harry@lob.com for additional details about a specific country.