the fix a flat stuff they give you is temp untill you get that tire fixed or replaced. just take the tire somewhere they fix tires. maybe you can have it fixed and not worry about getting a new/used tire.
and if they can not ask about their used tires but tell them you want the exact same size/speed rating/load rating.
That is 100% true. We, costco, can not fix a tire with fix a flat. Not only does it make the patch not stick properly, but it is also flammable and one big step to fix a flat is to "comb" the belts in the tire with a special bit which can (and I see it sometimes when I do it) which can create sparks. This is why a lot of tire shops will not touch a tire with fix a flat in it. That tire, at costco, is deemed not road worthy. Which at that time, you will need to replace the tire....or plug it yourself using those rope plugs you can buy anywhere. Which those suck too.