I've attatched a picture of my stock 77 CB550F. The mods are; engine guards, windshield, luggage rack, and passenger back rest.
The bike you are looking at, has several mods, wheels, exhaust, seat, luggage rack and backrest.
The seat appears to be from a K model which has a shorter fuel tank than the F models, and this makes it fit poorly.
The tool kit is fitted into the rear of the seat on the F and on a tray in the frame for the K. I expect you won't be getting a tool kit with the bike and worse, no place to put one when you get it.
The seat should open and close freely, unless your luggage rack prevents it. The K seat either bends or scuffs the tank badly on the F, if "adjustments" are not made.
The F carbs have the leanest settings of all the 550s, (save the 77-78 K models due to different carbs types). Simply swapping to low restriction 4 into 1 will result in lean settings. You should try to determine if the carbs have been adjusted for the replacement exhaust. If not, you may not be able to drive faster than 80 or 90 MPH, or encounter a lean condition at those speeds.
More important than a tank dent is whether it is clean and rust free inside.
Check to see if it has an oring chain (it should not) and if there are any oil leaks in the front chain sprocket area. (O ring chains can chew up cases/seals.)
Other than that, it looks like a pretty clean example. $1400 is OK if you want to and can drive it as is. But, if you are going to make changes, add that to your cost of ownership. The hack adaptation to the seat bothers me the most.
Cheers,
