Botulinum Toxin in Home-Canned Green Beans
The only way to prevent botulism in canned foods is to either make it to acidic for the spores to survive, or to pressure can it using the right equipment at a temperature of 121C for at least 3 minutes. If this hasn't been done then it could be full of botulism, in which case simply cooking it above 80C for say 30 minutes just to be sure (that's double the 15 minutes I've seen recommended on some sites, I'd take no chances) - as you say will destroy the toxin. If you eat it right away afterwards then you'll in all likelihood be fine, it takes a couple of hours at least for enough toxin to build up to be harmful, even in ideal conditions for it to develop. 

However, if there was a chance that there was botulism in home-canned food given to me I wouldn't take the risk. Even though I know scientifically that I would be safe by following the above advice I wouldn't be able to enjoy the food, every bite I'd have nagging worries that I'm poisoning myself. If I was starving I would in a second of course, but I can walk to the corner store and buy all the food I want so why take the risks? 

I wouldn't hesitate to try home canned food made by someone who knows their stuff, but if there's any doubt of the provenance of home canned food then the best advice would be to throw it away.