The only company showing up in a google search for Arlanda private transfers to Stockholm is Suntransfers. I've seen some trip advisor comments (mostly favorable) but only in a few other locations and only a couple in Europe..none in Scandinavia/ Stockholm. From reading other comments it appears the company is a broker of sorts between customers and drivers in the desired location. They have alot of reviews from something call 'Trust pilot' which I have never heard of.
Has anyone used them recently? Also..any other private transfers people might recommend? (Even the 'recommended' taxi services have me a bit nervous.)