Following the lead of the previous two posters, I rarely buy apps that don't have a paid version, and I often buy the paid version - with millions of apps on the iTS I don't see many non-game apps getting updated (how many PDF, note-taking, or calendar apps are there now?).
I take some time to read up on related apps - if they're abandonware, what's the point? I avoid developers based in Asia, mainly due to some of my work involving Federal funds but also partly due to seeing too many "stories" about hacking/breaches/etc. and not having any recourse - if the data source is housed overseas - there's no way in heck they're getting my 99 cents.
I avoid anything that Yahoo is involved with - too many abandoned products. And, if the dev doesn't own the data, their access could get revoked at any time because they're not paying the bills or the TOS changed.