I'd say if it's just bloating they have and not the pinecone effect in the scales which occurs in dropsy, then your advice for less feeding and more water changes is good.
Next time someone mentions their fish is bloated, make sure to ask if the scales are sticking out like in the picture above. Then you'll know which advice to give. Though there isn't really any known cure for dropsy, other than using the epsom salt baths to reduce water in the fish and try to make them comfortable until the end .
Advising to get a bigger tank also will help vastly. Exlain how their fishkeeping will actually be
easier in a bigger filtered tank. If they have a tiny bowl they have to change water every couple of days to keep the fish healthy, and it has no space to swim
In a 5 gal +
with a filter, they'll only have to change half the water once a week , and if they do it using a syphon they can clean the gravel and remove water at the same time. Doing two jobs at once and without having to entirely empty the tank or remove the fish. That will take less than 15 minutes out of an entire week.
Just a really big critter keeper ( the biggest size you can get ) is good and they cost less than full setups of glass tanks
if expense is a problem, so at least the customer will feel a little less like someone is trying to sell them the most expensive tank in the shop. I'd say advise to get a bigger tank second hand but I suspect your bosses would not appreciate that.
One like this is around 5 gals and not vastly expensive either ( though it say's for reptiles this can also be used for fish )
http

/lllreptile.com/store/catalog/reptile-supplies/kritter-keepers-and-cricket-containers/-/extra-large-herp-haven-critter-keeper/
If they mention supposed space issues ( almost entirely likely to be false as the chances of them having bothered to move things around and make space are virtually nil ) , A medium or large critter keeper
- for example - WILL fit on a bog standard kitchen worktop for example , I've done it and my kitchen is small , a hex tank WILL fit in 12-14 square inches of space. Anyone can find that amount of space somewhere.
A basic cheap sponge filter and pump, heater, bigger tank, reduced feeding and weekly water changes plus plenty of plants will all keep a betta very healthy and happy. And since they bought the fish as a pet one would presume a healthy happy pet is what they want.