Is this common practice or a even a good business model to people market their services through photography, facebook content, market research, etc?

If I'm reading this correctly, you're essentially asking if there is a market for marketing services.

To which the answer is a resounding 'yes'. Effective marketing and sales is essentially giving people money.

If you are wondering whether photography and facebook content is effective, there are plenty of people who use this alone, or to augment other efforts. Success is more dependent on the ability than the channel selected, in my humble opinion.

The easiest way to get started with something like this if you aren't 100% positive on your ability to deliver is to do it for free. The only risk is your own time.

This also gives you an opportunity to base your price off of value. Many people start out arbitrarily determining their worth and start charging per hour. With this, you might discover 5 hours of work yields $5000 in revenue for a client, which you could easily charge $1000 for.

You just started making $200 an hour.

If you choose to go this route, I would be careful with choosing your first test client. Some types of businesses (fashion retail for instance) are heavily influenced by photography while others (industrial chemical manufacturing) are not. If you choose a category without a lot of leverage you will have skewed results on the value your talents can produce.

Helping people market their business is always a good business model. The hiccup you may run into is the value you bring and the price you can charge.

One of my passions, for example, is helping small business owners with marketing their business; the problem is that I can charge X per hour, based on my demand, but those I am most passionate about helping can only afford Y.

You want to provide a low-risk offer to these customers, I assume "low-risk" to be a low dollar amount initially. This traps you into a low margin or low hourly rate (unless you systemize or automate this process).

I'd love to talk more -- sorry your question was pending for so long without a response.

-Shaun

Using Photography for marketing can certainly be very effective.
Content and their ads on social networks can generate some market however engagement for continuous usage of services is critical to success of client's venture. Ads can't buy engagements unless product services & features are creative or outside app marketing campaigns (instead of ads) are gamified in a indirectly relevant mechanism.
The most activity mobile app user does after texting and phone calls is Take Photos.
I would suggest to create a gamified campaign around taking photos of landmarks and reward those prospective users for taking 3-5 photos, social sharing etc.
Reward something simpler like what they can physically take home or share or use while traveling etc.
now once the campaign is over, notify all the participants to social share and also introduce your actual client's product/services. There will be a great chance of these users becoming your client's genuine customers and continue using your product.

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Good luck.
Best,
Shail