I can tell you as a "hub" that this seems to be regional as to how it's handled and I posted a topic related to this recently.  In the Northeastern states, unless it's back in the 30's (but sometimes there's no limit), we're usually charged for a current or two owner - whatever was ordered.  Others have a set year limit.  We have a client who is used to their searches turning into fulls so if i feel we're undercharged and there's room to pay the abstractor more while still giving the client a fair price - i do.  Some people sell themselves short for their efforts.

A few abstractors charge by link which can make it difficult to gauge costs to the end client.  This intuitively makes the most sense to me but there are times a current owner happens to go back 5 links within a few years and upcharging our clients on a search to 2005 is going to get pushback.  Other times the current deed is 30 years back and depending on the state, that can mean an easy search (MD) or a more difficult one because you're "slogging through microfiche and old books."

I don't think there's any easy answer when you're dealing with different states.  It's how tech friendly the state is, how well kept the records are which determine the time spent on a search.