Indents?

J 💗💙👼🏼💙

When using pregnancy tests how do you guys know if its an indent? I've had 3 babies and had faint lines with each, other than that every test has been completely negative. Ive used different brands as I usually grab whichever test I can get at the time. Is it really common? Ttc baby number four after a loss and I don't want to get my hopes up for nothing x