Assuming you've read Part 1 and Part 2 here we go with Part 3.
Sales Tax and Due Diligence in a small business purchase: Make sure the seller provides you with the Sales Tax Reports for at least 3 years. Double check those with the reports filed with the state. It is pretty unusual for small business owners to over-report sales and pay taxes they don't owe ,so this is a good source for determining the minimum sales level. If the sales tax reports and payments are not up to date seek legal advice on what effect that could have on you if you purchase the assets. In some states the sales tax "chase" the assets and you could be in for a surprise when the tax man shows up for old taxes on the assets you just bought.
If you are working through a business broker they probably already have the sales tax reports an can provide them to you in due diligence. But as always, trust but verify. Cross reference with the official state reports.