After remove the cart2quote extension error showing..
Invalid backend model specified: qquoteadv/catalog_product_attribute_backend_qquoteadv_tiercost
Please check the issue.
Solved! Go to Solution.
In your database find the eav_attribute table and find a row that contains qquoteadv/catalog_product_attribute_backend_qquoteadv_tiercost and remove that row.
You may have similar errors if the module created multiple attributes so it might be easier to run the following SQL to remove them all.
DELETE FROM `eav_attribute` WHERE backend_model LIKE 'qquoteadv/%'
Make sure you backup your database before doing any of this.