What exactly does "deceptively big/small" mean?

[BarkisIsWilling]

Why would you say a bag was "deceptively big" and can contain your guitar?

What does a "deceptively small house" signify?

Hmm, good point,not so clear when you think about it.
Is something deceptively small if it looks small but isn't or is it deceptively small if it looks large and isn't?

Hmm, puzzling. Maybe it would help to use a different verb? EG The bag appears deceptively small.

You need to ask an Estate Agent. I think a deceptivly small house would look impressive form the outside, but only be large enough for a hamster inside.

I understand bungalows can be deceptivly big.

I have always HATED these phrases -- WHAT do they mean? Why can't they just say 'tardis-like' or 'disappointingly cramped once inside'

There was a house near where I used to live that looked very small - it had been crammed in with 4 or 5 others in the space where one used to be - I never saw inside, but I think it must have been bigger inside than it looked, because it was called 'Tardis'

I agree with you all. Why can't people say things like "bigger or smaller than it looks"?

Apologies in advance to those who may not class estate agents as people ;)