Ok, unless his baseline weight when you got him was upwards of 2500g, it sounds like he's lost enough to be concerned about.

To start with, I would double-check all his husbandry. Ideally, you want 2 hides that are identical in size and small enough for him to feel snug when he's in them. What are your temps: ambient, cool side, and warm side? Humidity? You can find care sheets with the optimal ranges for each on this site. Is your heat mat on a thermostat? What do you use to measure your temps: IR temp gun or probes in the viv? Where are they placed? What substrate do you use, and do you know what the previous owner used? If he ate for the previous owner, you might try duplicating as closely as you can whatever environment he was living in previously.

Other things to consider are how often are you offering food? What prey have you offered, and is it what the previous owner fed him? Have you tried a variety of prey items? Is he in a part of the house where there's a lot of activity? How often is he handled? These are factors that may influence his level of stress and willingness to eat. In general, to decrease his stress level, you want to minimize your contact with him, and offer food less frequently than you would a BP who's on feed. Do a couple of searches on the site: there are many threads with similar scenarios. You'll find lots more information and advice, from folks with lots more experience than I have.

Hang in there & good luck,
Karen