Truth time: Many artists experience feelings of financial stinginess when it comes to hiring a photographer to document their artwork. If you have secretly felt this way and insisted on taking your own sub par photos here's another way to think of it.
1. Every time you pay a trusted expert to document your work you are investing in promoting the best and most professional version of yourself and your artwork. I always feel good about this expense.
2. Make sure that whoever you hire is recommend by other artists.
3. You should be able to see examples of some of the photos of the art documentation that they have done. Make sure that the photo are for art documentation - this is a very specific skill.
4. Especially for large work - it is very hard to capture the details. If you really can't afford to document your work then perhaps save your money and only hire for documenting large artworks.
5. If you have a website to show off your portfolio what is the point of sharing crummy photos? Make sure that you have excellent photos of your work available for potential clients to see on your website.
Along with these photos you can consider taking extra photos that help people see the scale of your artwork. See examples in this article: Creatively Showing Scale In Documenting Your Artwork