I think That they may not change the pistons unless there are undersize. they should at least hone it and rering. ,Ill bet though that the pistons are undersized and need replacing. At some point your going to have to trust them. and if they screw you then they have to look forward to seeing you again and often. Ive been in a situ. like this and they replaced the short block,but it was a ford. with .030 oversized bore , with standard pistons and rings, Ford new about it long before I found my issues.
They at least need to hone for a new cross hatch pattern to seat the new rings. Hopefully they measure the bores properly!!