Rent from a Strings shop. Usually the school has a list of local options. The store can service it if needed and give a loaner if necessary. Also most allow size trade ups. We've been very pleased with Day Violins near the Chantilly post office. Also if you are low income the school system offers a very low cost rental program.

Don't buy. Your kid will grow and need a larger size anyway.

Rent from a luthier.
Not a music shop.
Not a rando.

You should rent, OP. Go to Foxes violins (VA) or Potter's (MD). Your kid might decide to quit and then you won't know what to do with the instrument. And if you rent from a luthier, the quality of the violin will be much higher than any low-price violin you'd be able to buy from someone. They rent out violins in the $700 to $1K range, I believe, for $50/month, depending on quality. If you insist on buying, please do your due diligence and research the quality of the instrument. Don't buy something cheaper than that, it will sound awful.

Chuck Levin in Wheaton

Most kids rent when they start out. It's not expensive. You should also try your local community groups on FB or NextDoor.

Does anyone have a violin (for 4th grade music) they are looking to part with? Thank you!