You need to ask yourself what you are looking for in soiland not take someones word for what they are selling. "Topsoil" is simply the top 4 to 6 inches of soil from someplace so ask the seller if they will give you about a cup of that soil so you can see what it really is. Then test it. This simple test can help you determine that.
Soil test for organic matter. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it stand for 24 hours. Your soil will settle out according to soil particle size and weight. For example, a good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top.
Many people think "topsoil" is loam when it seldom will be.

Whatever you decide, you need to incorporate the new soil into the native soil so you get drainage.

Dan

I don't usually disagree with Dan about any of the advice he provides, but I am going to offer a different opinion this time :-)

One of the primary benefits of raised bed gardening is that it enables the gardener to garden under soil conditions that makes inground gardening challenging - like with heavy clay soils, poor drainage, inappropriate pH, etc. So the 'need' to incorporate the existing, underlying soil into the raised bed soil does not necessarily track. By definition, raised beds offer improved drainage over inground soils -- just by virtue of the soil level being raised but also because raised beds do not offer impervious containment and because the soil tends to be of fluffier, lighter texture; i.e. 'fast draining'. So the mixing of the two soils is not a requirement. However, if your raised beds are not deep, the underlying soil easily workable and you are interested in planting deep rooted plants or veggies, incorporating the two may be desirable.

As to what to fill them with, it depends on what you can find easily, locally and inexpensively. If you need a quantity, bulk soils will always be cheaper than bagged soils. And most bulk soil providers will offer something called a 'garden planting mix' or a '3-way mix' that is pretty much an ideal blend for a raised bed. Typically it is a mix of loam (sometimes 'topsoil'), some sort of compost or composted manures and a drainage enhancer - could be bark, sawdust, sand, even perlite. In lieu of that, try a 50-50 mix of 'topsoil' (or whatever generic soil they offer) and compost. And make sure the stuff is well-blended.

Because raised beds typically offer quite fast drainage compared to inground soils, moisture retention is sometimes critical. In hot weather, raised beds do tend to dry out faster. Mulching is typically the best way to reduce evaporation and conserve moisture but frequent watering may still be required anyway.

Thank you all for your welcomed advice. This will be my first time with raised beds. Trying to make less newbie mistakes as possible.

Well, gardengal48, I would like to ask you something about the mix you recommend. I find myself in the position of needing to seriously top up the soil in my one raised bed, which is a perennial herb bed. The soil has sunk so much that I'm sure I'll kill the plants if I don't dig them out, top up the soil, and re-plant them at the new level.

I'd made my own mix for these beds, out of topsoil, (commercial, bagged) composted manure, and peat, and the first year it was absolutely great, with almost no shrinkage. I thought I was home free. But then, last year, it shrunk like mad. I finally concluded that I really had far too high of a percentage of organic matter, and that if I'm going to have a perennial herb bed, I'm going to have to have a higher percentage of soil, and a lower percentage of organic matter. I asked about it in this forum last year, and most everyone seemed to agree.

So...while the 50/50 bulk loam/compost mix that my local garden center offers sounds quite attractive, I fear that using it will put me right back in the position that I'm in now. Yet...not adding any organic matter at all seems like a poor idea. But, on the third hand, herbs generally thrive in poor soil.

The raised bed in question is built on a slope, up against the neighbor's concrete retaining wall. One end of it is quite deep, while the other end of it isn't actually raised at all. I've seen shrinkage all along the length of it, but of course the worst of it is at the deep end of the bed.

So...this year I'm faced with the prospect of digging up every last plant in that bed, and re-planting them all. I'm not looking forward to it. While I'm at it, I'm going to raise the whole thing by another row of stones, since we "hit ground" before we made it to the other end of the yard. Maybe it's all for the best, but I hope to never find myself in this position again.

liera, I wouldn't recommend that 50-50 mix for herbs. They don't require anywhere near that much OM in the soil. In fact, I'd hesitate to recommend that mix for any type of perennials or permanent plantings. That's a relatively standard mix for seasonal crops or veggies that tend to have a higher nutrient demand and pull a lot of nutrients from the soil. And because these are annual crops, it's not an issue to top off each year if needed.

When adding to any sort of permanent landscape planting I'd go with a 3-way mix. This is the type of soil mix I use myself and after allowing for settling, I've never noticed any significant shrinkage.

gardengal48, some fruit plants do better in poor soil.
Not dead soil, just lean, not so rich soil.