As a professional, you should hold yourself to a certain standard and also employ the use of other professionals. Veterans in the real estate industry will swear by using professional photos. Even with consumers, the first thing they see online will be a photo. If the photo doesn't capture their attention, then it will be glossed over.
With that said ----
When is it okay to NOT use a professional photographer?
1. You are a Professional Photographer Yourself
Photography is a skill that many people have picked up and even leverage as a side gig. To be clear, owning a "professional camera" does not mean you can take professional photos. Understanding the composition of your shots, how to use your camera's settings to take the best exposures, and post-processing them in a way that highlights natural light of the home is not really something an amateur with a DSLR is trained to do.
2. Foreclosures Maybe?
Foreclosed properties are sometimes neglected. Investing in photography to capture this might not be the best idea. You should still use photos to provide an accurate representation of the property. It just doesn't make too much sense to outsource this task.
3. You Are in a Small Market
In rural areas, there might be less competition. So perhaps you can get away with not using some of your commission on lower-priced properties. That said though, you can absolutely stand out in a market that doesn't care about high quality photos just by having high quality photos. It is good customer service, and will leave a good impression (and future referrals) on your current clients.
Need more convince that you shouldn't use DIY solutions for your business? Maybe this article will help.