As always, only the context may say the actual meaning of this sentence. Anyway, taken by itself, the apparent meaning is, as in the first translation given, “I had to sell all my things to buy this car”. Moreover, the use of the imperfetto rather than passato prossimo or passato remoto tends to suggest that something else happened next. Say,
Dovevo vendere tutte le mie cose per comprare quest'automobile. Poi però mio cugino mi ha prestato i soldi.
That would be a so-called “imperfetto di conato”.
The use of imperfetto indicativo as an alternative to tenses of condizionale or congiuntivo is more frequent in other kinds of sentence, especially conditional clauses. “Se lo sapevo non venivo” is a more colloquial variant of “Se l'avessi saputo non sarei venuto”.
(By the way, as you see, conditional is a mood, not a tense, and has its own imperfect.)
There are other contexts in which you'd use an imperfetto indicativo as in the sentence given. For instance, when telling dreams and the like: that sentence might be part of such a narrative. For this one, the “conato” one and more, a good source is the entry on imperfetto of the Treccani Enciclopedia dell'Italiano (in Italian).