Not let peope in a group who where not involve access to modify a bill
I don't think that people that where not involved in a bill (even in the same group) should be able to modify it. Also, since everybody can modify anything, it would be good if you kept a log of transactions, ie: " John changed the total from X to Y"
We allow members of a group to edit all bills in that group because we think it makes it easier for people to correct problems and fix other people’s mistakes. We think this is pretty important – otherwise, it can be a huge hassle when one person accidentally enters something incorrectly.
You can see a record of recent changes in your account by visiting https://secure.splitwise.com/#/history, or by clicking the flag icon in the middle of the top of the page (in the green navigation bar).
AdminSplitwise Support (-, Splitwise) commented
Yes, but what if Fred was left out of the bill accidentally, and actually should be involved? We've seen a number of cases where people are included or not included on a bill by mistake – allowing all group members to edit bills allows users to more easily fix those sorts of mistakes.
Yes I agree on letting people modify it in case of error, however if in a group there Is John, Mary, Chris and Fred, but on this expense only John , Chris and Mary where involve, how can Fred having access to modify it help?
He wasn't involved, and thus has no business modifying that transaction, at least thats how I see it.