Upward Mobility: Highly variable depending on your office. Not much structure or organization. Some divisions are better than other. Better if you're willing to relocate.
Poor work-life balance, especially during the busy spring/summer season. Expectation is 50hrs minimum usually more like 60hrs. Again varies depending on office and rep.
Unneeded Tree Work: Varies depending on your rep, but sometimes you're going to do something that wasn't needed. Either the customer wanted it done and the rep was happy to make a sale or, and this is what really bothered me, sometimes your rep needs to make their numbers. They're going to send you out some little old lady's house and have you pump $2000 of fertilizer into a bunch of plants that really don't need it. The work you do is rarely true arboriculture.
Equipment: Varies from office to office, but sometimes employees have to provide their own equipment. This practice is common for the industry, but personally, I think they should provide equipment. Sometimes you get jobs that are going to trash your equipment and externalizing that cost onto their employees kills morale.
Pay trends on the lower side: Very hard to make ends meet without overtime. Pay raises are often hard to come by. The tree care industry really needs a union or some sort of workers advocacy group.
High turnover: Its a hard job, some people don't hack it. But the vast majority of workers come in, get their certifications, and they leave to go make more money elsewhere.
Comp Time: Little to no vacation time, no sick days.