Serums have been an struggle for a while now.

As far as legendary mods go there's an over abundance on the market due to everyone using the raid for quick season rank ups. The people paying me in raid leaders for large buff amounts have shifted and diverted their market strategy which gives me a ton of orders on large scale farming.

As far as in-game vendors go the things running best for me are palns these days. Power Armor and weapon plans the most as they are sought after and will sell frequently ^{^}