Wow, I'm surprised a group of people predisposed to gambling in vegas are so risk averse when it comes to their taxes.
I'm no expert but we have two home businesses and my wife expenses a laptop every couple of years, because they are cheap and don't last very long. We have a complicated return with a lot of deductions and have never been audited I think if you buy a basic $400 laptop and not some fancy gaming machine, almost any business nowadays could reasonably be assumed to use a computer to use it for turbotax, banking, paying bills, printing out invoices, etc and I don't see how this could be considered a red flag, except maybe for a child's lemonade stand (who probably didn't even make enough to pay taxes anyway).
Also the IRS has to balance the cost of auditing (which isn't free) against the risk that they won't collect anything from you. If your $400 laptop is used 50% for personal use, the deductible amount is 200 x your tax rate, vs 400 x your tax rate if you declare 100% business use. So if your tax rate is 33% you are looking at evading $66 in taxes. If you are amortizing the cost over the life of the laptop it would be even less. Also I don't think audits are usually done in person where they would come and inspect your property (according to my accountant). I can't imagine the IRS would come after you for a computer - and it would be hard for them to prove what the percentage for personal use should be anyway. That is almost certainly less than it would cost them to audit you and they have MUCH bigger fish to fry. That said, if you are doing something else that is likely to be an actual red flag - such as deducting some large expense two different ways or taking a tax credit you aren't entitled to, or deducting to the point of having much less income than other people who have similar businesses - the chance of being audited is higher.
If you have property and can demonstrate that you are using it in a business capacity, and have claimed the legitimate cost, according to my accountant it is fully deductible. Even if it weren't, I imagine the laptop is small potatoes compared to the cost of your auto mileage, insurance, cell phone service, space in your home that you use for the business and the business' share of home utility expenses, and the many other expenses you incur and can also deduct.
Finally, remember that if you are audited and can document that your expenses are legitimate, you won't necessarily owe money to the IRS. That said, I'm sure an audit is no fun and you may have to hire an accountant to help you defend yourself. And if you do owe money, you will owe the difference plus interest.
Here is a good reference:
https://www.irs.gov/businesses/small-businesses-self-employed/irs-audits