Well, while there are some legitimate reasons to not show interior pictures, the most common answer is if the agent showed you the inside of the house there's no way you would every look at it because it is, well, disgusting. Really.
Other reasons there are no interior pictures might be because a) the agent can't get in, as in there's a hostile tenant or family member; b) the agent is really lazy, or c) the house is vacant and with all the rental scams going on it is best not to be broadly publishing that.
Over the weekend one of my buyer clients called me about a house that fell out of escrow but sure looked good on the outside. No interior pictures and priced low for the neighborhood. To be fair, the listing agent did note that it needs some TLC. Totaling down to the studs remodel would be more accurate. I'm not a mold expert but sure would be willing to bet this one has mold. And asbestos, And who knows what else. (BTV - buyer to verify.) And its in the Torrance soils area. Ouch.
Just standing outside the property the numbers we heard being thrown by other buyers were that it would take $100-$250K to do the remodel. For sure. But in this crazy market that doesn't mean it isn't a "deal" if you can get financing. Most likely a C6.