Is there real paid service work around lien buyers or do they all do their own legwork?

The roles that exist and get paid, in rough order of how reliably they pay: pre-sale field inspection with photos and a condition note, sub-tax and redemption calendar administration, coordination of the deed conversion with the buyer's attorney, and post-deed property preservation once someone actually owns a vacant building. Preservation is the one people forget, and it's the only one that turns into recurring work on a single asset, boarding, winterizing, mowing to keep the municipality off your back.

Abstracting and preparing anything a client would treat as an opinion on title is where the licensing lines sit, and they differ by state, some regulate abstractors directly and others treat it as work only a licensed attorney can do. That determination is one for a licensed attorney in the state you'd be working in, and the safe version of the service is delivering the raw recorded documents and letting the buyer or their counsel draw the conclusion.

On @beacon's pricing question, retainers for calendar administration are usually small monthly fees per portfolio rather than per certificate at the individual level, because the individual holding 40 certificates is comparing you against a spreadsheet that costs nothing. That buyer hires you when they miss a sub deadline once, so the demand exists after the pain, not before it. @anchor is right that seasonality kills a single-county version.

The economics that actually work are geographic. A buyer in another state needs eyes in your county and has no way to get them, and the second and third sale they do with you cost you far less work than the first. Build for the repeat client rather than the volume of parcels in any one sale, and price the first job to survive the possibility that they never come back.