Because the word QUICK tells how you can sell, it should be QUICKLY. QUICK is an adjective.  

It's/Its

This from the description of the update for the Prose with Bros app. In the second line, the wrong form of its/it's has been used. 

Lean/Lien

This from the FoxNews 16 app. LEAN should be LIEN. 

The apostrophe is used here to make a plural. Tsk. Tsk. Merriam-Webster accepts CAPRIS as an acceptable plural form. ChaCha, which I do not consider an expert source, says there is no plural form of CAPRI and that one should use CAPRI PANTS for the plural form. Either way, the apostrophe is incorrect. 

Cloths/Clothes

There is a missing E in CLOTHS. This one can be found at Arkadelphia Aquatic Park. 

Misplaced Modifier

The problem in this sign is the placement of the word DOWN. I think it would be best placed after the word   KEEP. Placing it after COST might also work. In its current location, the meaning is confusing. Are we to avoid running down the park, or are we to try to keep costs down? This one is in the showers at Arkadelphia, Arkansas' Aquatic Park.  

The apostrophe is unnecessary. This one is from Fuddruckers in Branson, Missouri. 

The apostrophe in the headline is unnecessary because the writer intends to say that there is more than one 3-year-old, not that the 3-year-old owns a walk. 

The period should be inside the quotation marks. 

This one is also from a student. It should read "No UNaccompanied children."

Syrop should be syrup. Thanks to a student who found this one in Greece. 

Run-on

Personifying the toilet is entertaining. A period after "Please help me out" would help me out by correcting the run-on sentence between what should be two imperative sentences. 

Split Infinitive

An infinitive is TO plus a verb. To sing, to dance, and to report are examples of infinitives. A few stuffy, old grammar types still hold to the rule that one should not split an infinitive by placing a word or words between the words of an infinitive. In some instances, I must confess, splitting the infinitive seems the most natural and logical thing to do, and it is awkward not to split the infinitive. This is not one of those situations. The word NOT could be better placed before the infinitive. 

This one is difficult to read. APPLE should APPLY. 

Colon

A colon should not follow a verb. 

Colon

A colon should not follow a preposition.

Subject/Verb Agreement Error

The verb STAYS should be STAY because there are two simple subjects in that sentence: TRADITION and COMMITMENT.  

Your/You're

This is one of the most common mistakes I see. You're means you are. Your shows ownership. I found this one at a Walgreens in Branson, Missouri. 

I found this one at a fireworks stand. It should say GUARANTEED.