Withdraw after each order
Do not keep a running balance on the storefront. Sized-to-order only.
Every deposit on Nexus sits behind 2 of 3 multisig, so buyer coin is not custodially held by the operator. But after an order releases, the buyer balance appears on the wallet panel as regular balance, not as multisig-locked. That balance is custodially held until the buyer withdraws.
Do not keep a balance on the storefront across orders. Withdraw after each release. The wallet balance you should keep is either zero (nothing pending) or exactly the amount for the next order plus a small buffer for network fees.
The reason is not that Nexus is likely to steal your balance (multisig closes the largest attack vectors, and Nexus has run two years without incident). The reason is that a balance you can only recover from the storefront is a balance you lose if anything happens to the storefront. Withdraw promptly. Store coin in wallets under your own keys.