Another thought.
Some garages when changing the oil, syphon the old oil out through the dipstick tube.
OK. This removes the old oil but it's not the proper way.
The correct way is to run the engine until warm, Thus stirring up any rubbish and sediment in the oil and also allowing it to drain out quickly.
Then remove the sump plug, and drain oil into a container.
Two things to remember. Let the drained oil settle and check for any swarf, ( Bits of metal etc. ) , this gives an indication of the engine condition.
Secondly, Dispose of the old oil at your council tip, and don't just pour it down the nearest drain.
Oh, and don't forget to replace the drain plug. ( It happens ).
chadad