It may well be the darndest thing you saw but did he explain how this koi got an ulcer in the first place?
Nines out of ten they dont just appear but are the result of either poor water quality overcrowding temperature fluctuation etc that have the effect of stressing the koi out and the bacteria present .
The bacteria in question being the Areomonas Hydrophila which results ecause of the above reasons the above, Baytril is my own drug of choice and the site of the injection again would be my choice, however these ulcers can be avoided and the way to avoid them is constant vidulance on the behalf of the koi keeper and to ensure the water is of the highest standards you can get.
This requires constant maintenance of the pond, water changes, water testing, maintenance of your filtration etc.
However I will fault this dealer in that the koi should have been first sedated injected and the wound cleaned before applying medication to the wound, we here in the UK use an ozonated gel called Koi Clear Gel.
It is in effect the holy grail of ulcer treatments and it clears an ulcer in just two applications, I introduced this on a South African website (it has to be bought in bulk)but the feedback we got from it was phenominal in that it does what it says on the box so to speak it cleared up every koi they had with ulcers.
If anyone is interested it may be an idea to mention it to koi dealers who may then bulk order from the UK.
It is based on Japanese human treatment with Ozonated gel (I tried it on a cut to my finger whch cleared in record time).
Once you have used it you'll never go back to any other treatment a tub though small costs £25.00 UKP's but this small tub will treat up to 50 koi and is well worth the money you pay for it.
It has one draw back and that is it has to be kept in the fridge when not being used.
I've linked this post into the website about it :-
http://www.absolute-koi.com/subcat2086.html
Ask your dealer you know it makes good sense
rgrds
Dave
