The guy who cleans them might know what they are, he will also be able to tell low or high impedance with a simple test, saw someone do it once but cant remember how now.
Unknow injectors can be a problem tho, i bought rb25det hi flow injectors off here, was told they had been cleaned and flow tested and would can with a written report on them saying so and they were 650cc, all were perfect apparently, received them in the mail but no report, the seller never replied to me so i had them cleaned and tested just to be sure, 5 were good but one was more than 10% out, the guy cleaning them said he could try to get them to flow the same but no gaurentee's, told him to do it and it all turned out good except for the fact they were 500cc not 650, at the end of the day i could have bought a second hand set of 550's with a better spray for a little bit more than the 500cc high flows.