yes they can.
bitcoin is just a social contrqct you can opt into buy using it.
it allows anyone to sell for bitcoin and have a guarantee from all others in the network they will sell to you for bitcoin.
if you dont have bitcoin you should start out by earning some first, but ...it doesnt prevent you by buying from somebody who trusts you to pay back later - thats always possible .... can even be a group, but its a individuals/group based special agreement