Think of short as a negative share position. To close it out, buy the shares in the market at the (hopefully lower) price. You've (1) sold at a higher price and (2) bot at a lower price - profit is the difference.
Mechanically, the negative share position is achieved by borrowing shares to sell. This carries an obligation to give 'back' the borrowed shares, which is satisfied when you buy in the market.
For us, the most frequent issue on our land line are out-of-country calls (so out of jurisdiction) trying to sell duct cleaning services. We've gone as far as booking a couple of appointments to identify the local businesses that use these providers, but nothing comes of the reports. Where the origin is foreign, there are still avenues for domestic enforcement but authorities appear uninterested - to me this is an easy way to increase the effective cost of foreign call centers that don't obey local laws.
Re. the number of machines, it's something I've encountered as an obstacle from a fair proportion of people I've spoken about password managers to. I think its more a perceived issue than a real one.
Just spitballing which systems I would realistically want access to passwords on, at a minimum, includes: personal desktop, personal laptop, tablet(s), cellphone(s), family (parent, sibling, in-laws, etc) computers, office desktop, office laptop.
In my case (many cases?), the latter two prevent software installation, so I would need to manually type from a manager synced on my cell. Which really is no different to what is required for 2FA - just a longer character string. Overall, a some setup and synch related inconveniences but not to a damaging degree, which is why I think this is more a matter of perception - once you think through where you're typing passwords it appears less of an obstacle.