Receiving unsolicited inquiries about purchasing our Fircrest apartments

We own a small complex in Fircrest and regularly receive letters expressing interest in the property (which is not for sale).  I'm very skeptical of these solicitations and always assume it's someone trying to get something for nothing (looking for desperate sellers, for example). The latest letter comes from a real estate advisors group out of Seattle and the letter says they are inquiring "on behalf of a family-run investment group looking to acquire multi-family properties in Fircrest." And "given the lack of desirable product currently listed on the open market,"... [their clients] asked them to contact targeted property owners directly. They claim their clients are "experienced and well-capitalized investors who live locally and are familiar with the marketplace," and they are "looking for long-term hold and will pay market prices for quality B+ to A locations." They indicate our property meets their criteria. Are these typically legitimate solicitations? How can we tell the honest outfits from the dishonest ones? (BBB didn't list any complaints against them.) Why should we believe our property is special enough to warrant this attention especially given the general difficulties in the real estate market and commercial properties in particular? Would appreciate some expert insight.