Your travel agent can charge you fees for changes etc. in addition to the charges the airlines make for changes (and any fare difference). It is reasonable IMO to ask for a breakdown of those fees (so you can see what they are specifically - my travel agent has no issue doing this for me). He wouldn't charge me 4 x fees for 4 seperate tickets - it is on a per person per trip (whether I took 4 segments on BA, or 4 segments on 4 different airlines to get from A-B-A)

I'd tell the guy you don't have cheques - not all banks issue them as standard anymore.