Many manufacturers claim their Ovens are "self-cleaning". Ovens naturally accumulate grease, which eventually turns into cooked-on carbon. You should not be ashamed of your dirty oven as the process of cooking within the oven will create grease. It is the same as limescale - it builds up well before you see it. I am often amazed at the amount of grease that I extract from an oven that actually looks quite clean. I think to myself, "this will be easy", and then it takes me so much longer than expected to clean the dirty oven.
The 'Self-cleaning" concept is a catchy sales promise at the time of an oven purchase. You are probably thinking that is exactly what I would say as a professional dirty oven cleaner! But let me explain why you have probably been mis-sold. If the concept of "self-cleaning" was so trusted why don't we have self-cleaning cars and self-cleaning dirty oven extractors and hobs?
The concept of "self-cleaning"dirty ovens rests on the belief that the specially coated oven walls will catch the grease. On a weekly or fortnightly basis, the manufacturer will advise you to turn the oven to full heat, and thus burn off the grease, which you can then wipe out as carbon powder. You will need to get your dirty oven to at least 350 degrees (many are limited at 270 degrees), and then you run it for potentially 3 hours for the grease to burn off, and fall as carbon powder. The stench of burning grease turning into carbon dust can be choking, and is itself a health, let alone fire, hazard.
Finally, the cost of running your oven at full heat for a few hours is expensive.
A professional oven cleaner will be able to easily and quickly remove the grease and carbon, without the choking fumes, potentially unhealthy effects, and return your dirty oven to a near-new showroom condition.
Shortcuts are never as good as a proper clean!