If I were to recommend that to a client, it could very easily result in a fine and/or suspension or loss of my license (I'm a board certified professional geologist in KY and TN) and lively hood of the past 20 years.
He isn't anyone's client. Frankly I think we have too much government and his well is one of the things most governmental agencies aren't into yet. If it were mine, I'd keep it that way and take care of any problems myself, to my satisfaction. It used to be the American way... he (and all others that read this now or years from now) is being given the info to act on free of charge with no obligation.
Many field screening methods, when properly executed, are quite good at confirming or denying the presence of e. coli in groundwater. I would have no reason to doubt your ability to properly execute one. To obtain an accurate count, as well as legally defensible data, I would rely on a fixed based lab for the analysis.
The EPA and most states' standard is <1 CFU (colony forming unit) per 100 ml sample of water; that's with a 50x microscope. So the number of colonies, or the count, isn't of any importance IMO. In residential if there is any number, the water is not potable. In commercial, you do 5 check samples. If any fail, it is not potable.
After great consideration, I think I'll steer clear of discussing your "smell" method. As you are also performing quantitative analysis, I suppose no harm can come of it.
If I collected the samples, I always smelled the water by spraying it from the boile rdrain valve on teh pressure tank into a small bucket. I smelled the air coming out of the bucket for any odor. The reason I did it was due to many people not admitting to, or forgetting an odor when asked about odors. Especially guys wouldn't mention an odor but then when I smelled something and mentioned it or questioned how long they had the odor, many times they'd tell me of their wife having complained about one for some time "but it doesn't bother me". So had I not done that, and sold equipment, they may not be satisfied but not say anything to me about it, just their neighbors, friends, coworkers and probably some strangers.
You'll forgive me if I remind you that the OP wasn't inquiring about e.coli but rather iron or sulfate reducing bacteria.
In his first post he said: I had a well done in March, 202ft down pump is at 100ft. The water is pretty clear but it seems like when the water sits for a few hours and then you turn it on it smells like rotten eggs.
You must be assuming that "rotten eggs" is from IRB or SRB only. I don't agree. He could have a contaminated faucet tip and if so, I can all but guarantee it isn't from any type of reducing type bacteria. From my experience, it very well could be caused by Coliform and/or E-Coli or other types of bacteria.