Some of this depends on the client base.  There are 3 primary sorts of clients that we have and we do deal with each a bit differently when it comes to pay:

1.  The "man off the street" client is the homeowner, lawyer, historical association or other individual seeking a full title chain (usually for a zoning permit, or building permit, or simple history on a home).  This client is a 1-timer whose good will can bring in future business by referral.  However, getting the client request in email with a clear, explicit written agreement to pay is the first rule of business and has ever failed to garner payment, so despite frequent offers by people to "pay up front", I never find this necessary with the Common Man.

2.  The regular corporate client who offers repeat business through ongoing contracts.  I no longer offer this as an option, as these aggregate firms take $250 from a homeowner, farm the project out to us for $100, and yet expect to get $250 worth of work.  It cheats the homeowner out of quality.  BUT, when we did do this, we always rewrote their contracts to offer our terms, usually to have the contract rejected.  The few that accepted and signed did so, and did not like the retainer on deposit requirement, late penalties, and added fees for copies that they wanted for free.  I guess that RTFD was lost on them.  lol

 3.  Corporate clients who normally use vendor agreements still approach us because nobody else can or will do the research, so they are forced to pay our set rates, instead of their $100 fees.  This is always uncomfortable & unpleasant involving whining and crying on their part.  We have them prepay the research cost, and offer them doc copies at-cost.  Since we can inspect, digitally photograph and otherwise abstract Official Records at zero-cost at the county offices, we have no overhead for this and so copies are optional, and they can get them from other resources cheaper, sometimes.

 Solutions:

A.  Watermark your report pages and records copies with copyright and address.

B.  Get everything in writing by email including agreement to pay.  Get the client's name, address, email, phone, fax and contact agent name in the same email chain and include the email history as an Exhibit / addendum to your report.

C.  Check the abstractor forums:  wait 30 minutes before responding or tell the client that you'll call back in an hour.  This will give you time to check out their reputation for payment.  If they look bad, charge more and have them pay 50% up front, or refuse the job.  Really.  Are you so desperate that you want to work knowingly without pay coming?  

D.  Don't get in the middle of crappy vendor agreements;  charge your rates for your professional services, not somebody's "vendor" rate.  Remember, the only vendor search you will get is into old microfilm, microfiche, and books prior to 1985, because they can't get title cheaply online.  Why work hours for a $40 set rater with copies included when the deed is in 1932?

 E.  Have them give you a retainer worth a few searches that you can put on deposit in case of their payment default.  They are businesses with money, and your fee should not be contingent upon any "close of escrow" event;  they can pay you.  The homeowners and buyers are NOT your client;  they are theirs.  Your client is the firm that contacted you for a search.