The owners association builds a reserve to provide for future expenses, in particular for the maintenance of the building. All owners pay into this maintenance reserve on an ongoing basis, usually by utility value. The reserve belongs to the association, not to the individual owner, and is not paid out on sale.
For you as a buyer the level of the reserve is decisive. If it is well funded, upcoming maintenance such as a new roof or a facade renovation can be financed from it. If the reserve is low, special contributions or an increase of the monthly charge may threaten after the purchase. Ask the property management for the current level of the reserve and reconcile it with the condition of the building.
Also watch for open contributions of the seller. If the seller has outstanding payments to the association, the owners association can, under the conditions of the WEG, reach the object that now belongs to you. Have it confirmed before the purchase that no open contributions exist. How to secure the purchase contract as a whole is covered in the post on the review of the property purchase contract before signing.