An important part of determining if you’re getting a good deal are the accessories that come with your earbuds. If you’re happy to settle for just the earbuds, that’s fine, but many companies will provide extra eartips or other goodies.
Additional eartips serve a couple of purposes, the first being comfort. Eartips can come in different sizes since we all have different ear canals. I personally have different sizes on different sides of my heads so I have to replace one of the eartips out of the box or earbuds will fall out of my ear. On the other hand, my wife has very small ear canals and has to replace the standard tips with a smaller option for her to be able to use earbuds comfortably.
Another factor in replacement earbuds can be sound quality. Generally, earbuds will come with one of three different types of tips, sleeves (soft silicon), foam, or hard plastic molds.
Sleeves come standard on almost all earbuds and provide decent sound and durability. They’re reusable for generally the entirety of the life of the earbuds and can be changed out at any time.
Foam tips provide more isolation and a more comfortable fit. Due to the better seal of foam tips, music can sound fuller and warmer, which may be more pleasing to the ear. Due to construction, foam tips will need to be changed out after a month or so and are not washable.
Hard plastic molded tips are custom to your ear and normally come on either the most high-end earbuds or separately from a kit you can buy. Molds can provide a perfect fit in your ear and thus provide excellent sound seal. You’ll normally only find these on high-end In-Ear Monitors, but some mid-range IEMs can be found that offer custom molds too.