There are a number of checks that can (and are) put in place in physical paper based elections that mean large scale collusion is needed to make large scale fra

There are a number of checks that can (and are) put in place in physical paper based elections that mean large scale collusion is needed to make large scale fraud work. 1) Observers at polling stations. 2) Sealed ballot boxes. 3) Observers from many parties and neutrals at counts. 4) Physical votes retained and recountable. It isn't going to be completely secure but if you measure the systems security by how few people you could rig an election with it is an order of magnitude harder [edit: to rig].