Im going to have to sort of stand up for these large retailers.
I have the misfortune of working for a Currys store, However look at it from their view (more currys than jessops)
We have a limited number of staff who need to be trained to be experts (as customers like yourselves expect... and rightfully) in everysingle area. Particularly in smaller stores where you cant have area specific staff.
We get paid minimum Wage, with a pretty ropey bonus system, we have more targets than you would believe, which if we dont meet they now will get rid of us within 2 months if we dont meet the target the following months.
The majority of staff will be experts in a few areas. Whilst i might know my fair share about SLR's and TV's i wouldnt be an expert in Whitegoods. However i do my best to help.
Jessops will be in a similar position, your never going to get alot of decent staff if you dont pay them right. There is only a small number of people in the country who would be experts in this field and want to work for minimum wage.
Ontop of which you get customers coming in and blaming a poor system or a select number of sales people on the whole store.
All of these stores have people that know their stuff and those that dont. But if you came in and no-one would serve you as they didnt have any experts in this area you would be equally displeased im sure. At least they let you try out the camera and lens, despite the miss-informed member of staff believing the TC wouldnt AF. Admittedly im not sure why a person working in a camera specific shop wouldn't know how to fit a lens correctly, but maybe she was new. At least you got what you wanted from the shop, now you can buy it online at a big reduction.