With all due respect to the OP, this is what being in business as a professional means. You have to deal with bullshit. Strange hours? Demanding clients? Haggling? - it's all part of life as a professional. The OP stated that she used to work at Shoppers Drug Mart. Retail is a lot more rigid in terms of hours, closing times, prices, etc. etc. Retail pays minimum wage, maybe minimum plus a couple of bucks an hour at best.
Here is my world as a so called professional.
1. Low price gets the job. Every time. The client puts out a scope of work, they solicit bids from qualified similar companies and he who bids the lowest gets the job. Now imagine if sex workers worked like this. Clients put out a shopping list, (BBBJ, DFK, COF, etc. etc. )and the only way you picked up work was by being the lowest price on the block. Second prize? Well unlike Glengary Glenross, there is no set of steak knives as second prize in my world. There's fucking nothing. It's winner take all. We can spend months preparing a bid for work. It can cost tens of thousands of dollars. And at the end of the day - second lowest price = zilch.
2. Even when you're low, the client will try to chisel you down before awarding a contract. How come your item for this is so much more than your competition? Your price for that seems high. What about if we pay you in 10 days instead of 30 (which really means 90), can you cut 2 points off your price?
3. Work hours? It's 24-7. Cell phone is always on and you have to be prepared to get on a plane at a moments' notice.
4. You planned a vacation? Too bad, this came up. Cancel your vacation. No, we won't reimburse you for your tickets. Talk to your boss about that.
5. Risk - huge
6. Liability - more huge.
7. And speaking of getting paid, it's supposed to be 30 days. Some clients, it's more like 6 months. Imagine providing your service and not getting paid for 6 months my dear. In the mean time, you've got payroll and overhead to cover. Does my client give a fuck? Nope. You should consider yourself lucky, there were 4 other companies vying for this contract and you got it. Consider yourself fortunate you're working for the likes of us.
8. Subcontractors. They make a mistake and it's my problem. Imagine getting a quote for a certain scope of work and then when it comes time to do the work, they charge you more because they fucked up. Too bad for me. Sure, I could go to the next guy, but his price is even higher. Problem is, I've carried the lower price in my estimate. Then the fuckers start demanding extra money for one thing or another from me. The client won't pay. So what do you do?
9. Vacation. If I get half of my allotted vacation per year, I'm fortunate.
10. Overtime pay? Does not exist in my world. You need to work to get the job done on time and on budget. (Preferably on budget.) If you need to work 12 hours a day 6 days a week, so be it. But you'll get the same pay every 2 weeks.
11. Ball buster clients? Yes sir. Lots of them.
So, to the original poster, I don't feel too sorry for you.
The only thing (as far as I'm concerned) crosses the line is abuse. No-one should have to put up with abuse. But everything else is par for the course.