i never encountered such a thing like save lock to account or something like that...
i never had problem loading other peoples saves, other than windows fucking up with the permitions in the programs folder
just copy the files to the right folder.. some games do save in my documents folder, others save in appdata, others in steam user data, but all you have to do is copy and paste.
there are some cases where you copy cfg files that may cause some confusion like someone playing a game configured for a 4k resolution screen, and the game will try to launch in that resolution and your screen goes mad
steam also has the cloud save sync thing, you may want to disable it to prevent some mix up like restoring the older save, maybe that's the issue you are facing?
tell ya what, send me a pm, i let you add me on steam and we can save swap to try it