In case there's no service book filled in and stamped I'd expect to see detailed bill with mileage noted.
You need to refer to schedule, most are inspect or tighten. Oil change yes, plugs too (but not necessary in most folks opinion). You won't be able to check 'inspect' or 'tighten' so it really is a little service.
Avoid word of mouth assurances, knock the price down if there's no proof,say £200.........
Note that 15K service should change oil, filter, plugs again (no!) and engine coolant. Rest are checks only.
Just me.