I wouldn't say the Op is planning on conning them, but I don't think, assuming that she's telling exactly their plans that it financially adds up, which then makes me wonder if there's more to it than she's letting on.
Cost of a garage on block round here is around £30k, you see them advertised between £30k-45k anyway.
Reduction in value of a house is over £45k, probably around £60k for one next to the house-and that would count as the majority of garages here are in a block.
So let's say she pays £45k, she's then got the expense of rebuilding it as double. It's roughly £1kper sq m I think building coats, or it was 10 years ago when we had ours built.
Double garage is roughly 3m x5m x2 (just looked it up) so another £30k on top.
So paying out a good proportion of £75k to just get a larger storage area.
Add an extra £75k to our house and you'd get an extra bedroom and probably a bigger garden you could put a shed in-or even a house with a double garage 😁.
So wouldn't it make more sense to move?
Now obviously she may be in a place where housing is cheaper, but then you'd be able to upgrade the house for less too.
So I think this is why people are feeling the neighbours might think she's trying to con them. Because financially it doesn't add up.