There are several reasons why you should or at least can justify raising rates. Some of the usual ones include the following (that are applicable within Upwork):
1. You've earned enough experience on the site (6 months, 1 year, and so on).
2. You have acquired a new skill and/or including a certificate you can upload to prove it.
3. You have satisfactory scores on the site (i.e. Top Rated badge).
I just raised mine, and looks like my bills raised theirs.
Association fees went up
AT&T raised their unlimited data access rates
The dog's vet raised theirs
So, I just say "Price increase due to increased costs in doing business ." Sounds like good suit speak.
When I was new to Upwork, (a whopping 13 weeks ago!), I started by pricing myself at what would payout as the lowest discount rate I offered through my current freelance business. I found after receiving several fixed price jobs (that actually translated to more than this amount), AND getting bonuses on top of it, I should raise my rate. I set it at double what the initial hourly rate was. After a couple of weeks and not getting near as much response, It lowered it to right in between - 1-1/2 times the original rate. This brought back the same response I enjoyed as a newbie, and I still get bonuses! A little trial and error is probably the best suggestion I can make. Balance the desired number of responses with the hourly rate.
Great question. When I started on Upwork, I cut my price by $10 an hour because it was still a good price (I was willing to accept). I wanted to get that first job.
Once I had a couple of five-star reviews and was working close to full time, I raised my rate back up by $10 an hour. Zero pushback from clients.
I think that demand for your services is the primary driver for your rates.
Also, you have to provide something that is better than your competitors. I am a writer, but I'm also a professional marketing coach. I interview my clients for website content and that makes me an easy choice for clients who hate to write. They love to talk about their business instead of writing a draft for me.
I strategize with clients as well as doing the writing, so that has even more value. The website content becomes a strategy in motion.
Think about this: How can you add extra value to your services? How can you stand out from your competitors?
For many freelancers, they do provide "extras" of some kind, but they don't build it into their profile.
When you increase the value (both actual and perceived) to the client, it's a lot easier to raise your rates.
In fact, helping consultants raise their rates is one of my specialties and it's included in my profile.