Non-owner wants survey
No problem. Just another survey.
While negotiating for a price and everything to sign a contract of sale is when it is decided who pays for the survey.
Anyone can get most any property surveyed for whatever reason and as long as you have an official survey order from them then you are most likely guaranteed to get paid or will have proof if you have to collect your fee by other legal means.
I've surveyed property that I did not have permission from the owner to be on his land. I simply did not get on his land and traveled on the adjoining property and all is fair at the monuments as long as you leave them as you found them as far as covering and putting the sod back in place or repair any holes in asphalt and such.
All of our contracts specify that the client is responsible for providing "suitable access" to perform the survey - i.e. keys to gates, dogs restrained, landowner's permission, etc. You are working with written contracts, right?
On the lines of surveying for clients other than the owner. Most ALTA surveys are for the perspective buyer.
As to @a-harris, in Oregon you can be (and I know those that have been) taken to the BOR for right-of-entry issues if you tie a monument on the line without contacting the adjacent owner.
Searching my memory, I recall that I have performed many surveys for non-owners. Assumed good intent.
There are a myriad of valid reasons that a non-owner may want to spend hard cash to determine boundaries, easements, and topography. It is not my task to inquire Why.
As always, we try to contact the occupant out of courtesy and and convenience.
I can't think of any statue or regulation that would prohibit it... beyond common trespass.
Here, it is NOT socially acceptable to pass thru a gate into a yard or patio without the occupant's permission. But that is a social thing, not a mandate by a government. Open land (no fencing or hedge rows) are kinda considered "open" to the public for non invasive travel.
BTW: the general public (American Tourists) seem think it is OK to just barge in, fenced/gated or not. They are looked on scornfully, but usually tolerated if they don't damage or litter.