when does this hobby become a liability?

No issue if you spend 10k at a Omega boutique.

You have no issue with two watches.

As long as you have watch as description on all sales.

If in US just join the watch thingemabobs that have meetings, bam your a watch collector.

Given the job that "professional" economists have been doing over the past 15 years or so, those who don't consider alternative perspectives do so at great risk.

Oh, and those who resort to ad hominem attacks invariably reveal far more about themselves than their intended targets.

When the Australian $ was at $1.10 there were guys buying boats for 50-60k from the US from regular joes like they were going out of fashion.

You sell a car or boat in the states any issues.?

You worrying for nothing

Most bought to use. I looked at one (Tracker bass boat) and would have saved 20k even with import costs but they make the hulls too thin for our waters in the NT ( minimum 4mm hulls needed for plate boats up here)

So you declare any capital gains on any of your watches lately ☕

As a practical matter, the IRS will match any Form 1099 received from eBay or PayPal to your tax return. So, if you receive one, omit at your own risk.

However, that's only half the transaction (proceeds). You also need to document your purchase prices. On another thread, there was mention of a spreadsheet format to keep track of purchases. Great idea!

Understand that Uncle Sam is only your partner when you win, when it comes to collectibles. If you can prove a profit motive for you hobby, then you can deduct losses in the bad years. But you'd better show a profit 3 out of 5 years, otherwise the burden to show profit motive is on you.

One other thing, if you are a hobbyist, your net gains from trading watches is taxable at a special rate for collectibles at 28%. Aggregate losses are deductible at a maximum $3,000 per year in excess of other capital gains you might have for that year. If you can prove you are a business, you can deduct your losses in full, but any profits are taxed at ordinary graduated tax rates, plus self-employment taxes.

The government is not your friend, at least in the US.
gatorcpa