The trial disguised as a free plan
The commonest pattern is a fourteen or thirty day trial presented as free, where everything works beautifully until the day it stops — usually mid-month with a customer at the counter. Check for a countdown anywhere in the product, and check whether a card was requested at sign-up. A genuine free plan has a usage limit, not a clock, and asks for no card.
The branded invoice
Some free tiers print the vendor's name or logo on the invoice your customer receives. That looks amateurish, quietly advertises against you to your own buyers, and is often only removable on a paid plan. Raise one bill and look at the PDF before you commit anything else. Your invoice should carry your details and nobody else's.
The export lock
This is the one that actually traps people. If a product will not let you export your parties, items and ledgers, then leaving means re-typing years of history and you are not really a customer any more. Test the export before you rely on the product, not after. Everything here exports to Excel on every plan including the free one, and we would say the same test applies to us.
The limits nobody advertises
Ask what happens when you add a second staff login, a second device or a second branch, and what happens to your data if you stop paying. Those three answers separate products more reliably than any feature list. A product that locks your records over an unpaid invoice is more expensive than its price, whatever the price is.