Stress
Remember our conversation about the poker game hanging above the laser sharks? Seriously, you take risks every day as an antiques dealer. In your first job, you'll be worked very hard to get competent with the day-to-day stuff, and before you know it you'll be spending money on behalf of the company. If you're not successful in flipping your first few purchases, you can probably say sayonara.
The higher you climb, the more responsibility you get and the more flexible your schedule becomes. Ideally, you also become more confident and secure in your position. As with any risk-related game, you can always hit a bad streak. If you hit one while running your own business, this could create some serious money issues. If you can keep a cool head, you should be fine...but as a career, antique dealing is not necessarily the most secure career path.