diff --git a/web/components/manaboard.tsx b/web/components/manaboard.tsx
index 08fa126c..2e7376c0 100644
--- a/web/components/manaboard.tsx
+++ b/web/components/manaboard.tsx
@@ -84,6 +84,7 @@ export function Manaboard(props: {
                         holder={user}
                         value={values[index]}
                         createdTime={createdTimes[index]}
+                        allSlots={users}
                       />
                     </Row>
                   </td>
@@ -114,8 +115,9 @@ export function BuySlotModal(props: {
   slot: number
   value: number
   createdTime: number
+  allSlots: User[]
 }) {
-  const { slot, title, holder, value, createdTime } = props
+  const { slot, allSlots, holder, value, createdTime } = props
   const user = useUser()
 
   const [open, setOpen] = useState(false)
@@ -133,6 +135,14 @@ export function BuySlotModal(props: {
   //   await buyLeaderboardSlot({ slotId, reassessValue: newValue })
   // }
 
+  // If the user already exists in a different slot, forbid them from buying this one
+  const userExists = allSlots.find(
+    (u, index) => u.id === user?.id && index + 1 !== slot
+  )
+  const errorMsg = userExists
+    ? 'Sell your other slot first (by revaluing it to M$ 0)'
+    : ''
+
   async function onBuy() {
     if (user) {
       // Start transactions, but don't block
@@ -187,7 +197,7 @@ export function BuySlotModal(props: {
             onChange={(amount) =>
               setNewValue(amount && amount >= 1 ? amount : 0)
             }
-            error=""
+            error={errorMsg}
             label={ENV_CONFIG.moneyMoniker}
           />
 
@@ -200,7 +210,11 @@ export function BuySlotModal(props: {
             </div>
           ) : (
             <Col>
-              <button className="btn btn-primary" onClick={onBuy}>
+              <button
+                className="btn btn-primary"
+                onClick={onBuy}
+                disabled={!!errorMsg}
+              >
                 Buy Slot ({formatMoney(value)})
               </button>
               <div className="mt-2 text-sm">
diff --git a/web/pages/leaderboards.tsx b/web/pages/leaderboards.tsx
index 09281bb3..c8989dd9 100644
--- a/web/pages/leaderboards.tsx
+++ b/web/pages/leaderboards.tsx
@@ -156,7 +156,7 @@ export default function Manaboards(props: {
       // If new value is 0, that's a sell; reset to topTrader
       if (data.newValue === 0) {
         slots[slot - 1] = topTraders[slot - 1]
-        values[slot - 1] = slot
+        values[slot - 1] = 50 - slot
         createdTimes[slot - 1] = 0
       }
     }