It is possible to test between 300 to 500 items per day and fuse checks etc, as most plugs are molded now days so its just a quick flick with a terminal screw driver fuse size and carrier checked in a couple of seconds, with the current testers testing time of the machine is anything from two to five seconds depending on the type of test, but the biggest key to it is either having your tester setup correctly to store the data fast ie presets in the memory, iec lead, vdu, cpu etc so you dont have to type them in everytime.
But the biggest change came to the industry with the pda wich means that in a couple of clicks the data is input and is ready for invoice when you leave the site instead of paperwork that could take up to a month to process it can now all be emailed to the client instantly saving the need for office staff therefore cutting the office overheads so a cheaper price per test, with the biggest firms now charging approx 50p per test.
It has killed the one man band at a quid per test plus vat but im affraid thats technology for you and all the silly comments above stem from dinosaur's in the industry who havnt invested in decent testers or a good it infrastructure.
Im sure if you google the major players in the industry they all have the major accreditations, yes there are ex toilet bog cleaning firms who use unqualified staff and lick it n stick it engineers and should never have brought there way into the industry but as a test engineer of fiveteen years I have seen many good companys and engineers and worked with the company who brought this type of testing to the forefront of this industry and has paved the way for quick and convenient testing so instead of having to say to a client we can do a maximum of a hundred tests per day and your site at 50, 0000 bits is impractical to test it has allowed the industry to thrive and bring some well needed money back into it so future lives can be saved.
And my final point is I have even tested the nic/eic offices as well and we all know they wouldnt have cowboys in there own place.