Certainly. Based on the provided legal document, here are the key points summarized with references:

1. In auction sales, compliance with legal procedures is essential; failure to do so results in the sale being considered null and void, and the certificate of sale does not convey good title if law is not followed (!) (!) (!) (!) .

2. The validity of an auction sale can be challenged on grounds such as irregularities, breach of statutory provisions, or fraud. Even if a sale appears to be irregular, it remains open to the parties to raise such defenses in subsequent proceedings (!) (!) (!) (!) .

3. The sale certificate issued by authorities is not necessarily conclusive proof of title if the sale was conducted in contravention of laws or regulations, especially if there was no compliance with prescribed procedures like fixing a reserve bid or proper service of notices (!) (!) .

4. The principle of res-judicata does not bar a party from challenging the validity of an auction sale if the challenge is based on legal defects or procedural irregularities, especially when the sale is void ab initio (!) (!) (!) (!) .

5. A party can defend possession or title by establishing that the sale was a nullity, without necessarily resorting to a substantive suit, provided the defect affects the legality of the sale itself (!) (!) .

6. The absence of necessary parties, such as the municipal authority or co-owners, in a suit challenging an auction sale does not automatically invalidate the proceedings if the sale itself was unlawful or irregular (!) (!) (!) .

7. The law requires that notices of auction and service thereof be properly executed; failure to do so can render the sale invalid and the sale certificate void (!) (!) .

8. The legal provisions do not make the sale certificate conclusive evidence of compliance with all procedural requirements; therefore, a sale conducted unlawfully can be challenged and set aside (!) (!) .

9. The power of an appellate court under relevant procedural rules allows it to pass appropriate orders to prevent conflicting decrees and to do complete justice, even if some parties or issues were not directly involved in the appeal (!) (!) (!) (!) .

10. Challenges based on procedural irregularities, such as non-service of demand notices or failure to follow prescribed auction procedures, are valid grounds to declare the sale null and void, especially when such irregularities are established by evidence (!) (!) (!) .

11. The burden of proof lies with the party asserting the validity of the sale; if the evidence shows procedural breaches or illegalities, the sale can be declared invalid (!) (!) .

12. The law permits raising the plea of invalidity or nullity of a sale as a defense in a possession or title suit, without the need for a separate substantive suit, provided the sale was conducted unlawfully (!) (!) .

Let me know if you need further elaboration or assistance.